Is your MacBook Air battery or MacBook Pro battery not charging? Don’t worry. We will guide you step-by-step to fix the MacBook not charging problem. 

MacBook battery not charging - notification on Catalina

This guide is written by technicians and engineers who fix MacBook battery not charging issues hundreds of times every year. It covers all the topics from simple fix solutions at beginner-level, all the way to complex repair solutions at expert-level. It provides practical and comprehensive solutions to solve the MacBook not charging problem, no matter if corrupted firmware settings or hardware faults cause it.

1. What is MacBook battery not charging issue?

A MacBook battery not charging problem means that you can turn on your MacBook, but the charger will not charge the battery. In other words, your MacBook is mostly working well except for the battery charging function. The following symptoms indicate that you have a MacBook Air or MacBook Pro not charging problem:

  1. You get the message “Battery is not charging" in the status menu.
  2. You have the message “No battery available" in the status menu.
  3. You don’t have a green light or orange light on the MagSafe connector.
  4.  The status menu shows your battery is normal and fully charged. But if you remove the charger, the MacBook will turn off instantly.

Many people get confused between “MacBook battery not charging” and “MacBook not turning on”. A MacBook with battery charging problem can be turned on if you connect a working charger to it.  On the other hand, a “MacBook not turning on” problem means that when you press the power button on the MacBook keyboard, no matter you connect a working charger to it or not, you can’t see anything on the Mac screen, no chime, no light on the keyboard and no fan-spinning noise. In other words, the MacBook has no sign of life at all. If your MacBook can not turn on, see our article MacBook Won’t Turn On? 10 Ways To Fix It.

2. Why is my MacBook battery not charging?

MacBook battery charging system consists of four components: a charger, a battery, a charging circuit and an SMC chip. Any of these components gone wrong would cause the MacBook Air or MacBook Pro not charging. 

  1. MagSafe charger or USB-C charger. It delivers power to your MacBook and its battery.
  2. Battery. It stores power (charging) and provides power (discharging).
  3. Charging circuit. It converts the charger voltage to run your Mac and charges the battery.
  4. System Management Controller (SMC).  It controls the behaviour of the charging circuit including start or stop charging the battery.

Faulty chargers, faulty batteries and incorrect SMC data account for the majority of MacBook not charging problems. Fortunately, these faults are easy to fix. Faults in the charging circuit are hard to fix and we discuss it in the last section.

If you notice the Battery Status menu says Not Charging, and the message disappears later, your MacBook should be fine. You could see the temporarily Not Charging message for several reasons:

  1. You use a low-power adopter. The power adapter barely provides enough power to run your MacBook, but not enough power to charge the battery. For example, if you connect a Macbook Air charger (45W) to a 15” MacBook Pro (85W charger required), you could get the battery not charging notification. If you turn off the Mac or put it to sleep, the power adapter will start charging the Mac.
  2. Safety concern. If you connect your Mac to an airline power adapter, your Mac might not charge the battery, even if you turn off your Mac or put it to sleep. You can still use your Mac without draining its battery. For safety reason, charging a battery in an aeroplane is considered a risk task.
  3. Running high-performance apps. If your Mac is running high-performance applications such as video editing software and video games, the Mac battery may not be charged. If the apps demand more power than the adopter can provide, your Mac will combine the adopter power and battery power to run the MacBook in order to meet the high power demand. This is an Apple design feature to boost performance on demand. If the apps drain the battery too quickly, you may need to pause the apps and let your Mac start charging the battery. If you switch off the Mac, the adapter will charge the Mac much quicker.
  4. Extending battery life. Your battery may drain to 90% or lower before it begins charging again. This is a design feature to extend the life of your MacBook lithium-ion battery. You can turn off battery health management in Energy Saver preferences. We don’t suggest you change the setting unless you have a special need.

3. How does a MacBook charge its battery?

In order to quickly diagnose and fix the Mac battery not charging issue, you need to know how a MacBook charges its battery. There are two types of MacBook chargers: MagSafe charger and USB-C charger. Apple discontinued the MagSafe chargers in 2015-16.

Magsafe Charger

The output voltage of a Magsafe charger is fixed. A MacBook Air charger outputs14.5V. A MacBook Pro charger outputs16.5V, 18.5V or 20V depending on the model.

When you connect a MagSafe charger to the MacBook, the SMC will “handshake" with the info-chip inside the Magsafe connector to identify the charger type including voltage output, current output, manufacturer code and so on. If the charger meets the criteria, the SMC turns on the green light on the connector. This green light tells you that the SMC has successfully identified a suitable charger for your MacBook.

The SMC will also “handshake" with the info-chip inside the battery to identify the battery type including the working voltage, manufacturer code, current temperature and so on. Based on the data received from the charger and the battery, SMC determines whether or not to charge the battery and how much amount of current will apply to the battery cells. 

SMC will tell the charging circuit to start charging the battery if ALL the following conditions are met:

  1. The MagSafe charger has enough power to power-on the MacBook and charge the battery at the same time.
  2.  The temperature of the battery is normal and the battery is not fully charged.
  3.  The charging circuit detects NO over-current or over-temperature.

While the SMC controls the charging circuit to charge the battery, it turns on the orange light on the connector. The orange light tells you that the charger is currently charging the battery. 

When the battery is fully charged, SMC will cut off the current flowing into the battery to prevent overcharging the battery. The SMC then changes the light colour to green. This time the green light tells you that the charger has completed the charging task. The charger at the moment only provides enough power to power on your MacBook if the MacBook is on. 

USB-C Charger

The output voltage of a USB-C type charger is not fixed. The USB-C charger will negotiate with the MacBook to work out an optimal output voltage dynamically. A USB-C charger could output 5V, 14.5V and 20V depending on the situation. For example, a MacBook Pro USB-C charger will output 20V to charge the battery. When the battery is fully charged, and the MacBook is off, the USB-C charger will drop the output voltage to 5V.

There is no indicator light on the USB-C charger connector to tell you what is going on. But the principle of the MacBook battery charging system is the same, although the communications between the USB-C charger and the SMC are much more complicated.

More for advanced readers: MacBook charging circuit discussion &  MacBook power-on sequences

Armed with this knowledge, you are ready to fix the Mac battery not charging problem now.

4. Fix MacBook not charging problem step-by-step

Many factors could cause the MacBook battery not charging issue. Depending on the cause of the MacBook Pro or MacBook Air not charging issue, the corresponding solution varies from easy to hard. We will discuss the easy solutions first and the most difficult one at the end. Some hardware-related issues require specific equipment and(or) spare parts. At the beginning of each section, we will mention the difficulty level of the fix and equipment and(or) spare parts required for the repair. So you can estimate your successful rate based on your skill. Good luck!

4.1 Check charger output voltage

Difficulty level: Beginner

Spare part required: Spare charger will help 

If your MacBook charger is not working, of course it can’t charge the battery. So you need to make sure the charger is working fine.

First, you need to make sure that the power outlet is ok. You can plug in a phone charger or a lamp to the power outlet, or plug in your MagSafe charger to another power socket. This simple step lets you know that the power outlet is working or not.

Don’t forget to check the power cord connection on the charger. The Apple adapter consists of two parts: the MagSafe charger and the removable power cord. Make sure you insert the power cord to the MagSafe firmly. 

Next, inspect both the input and output cable of the charger carefully, starting at one end and work your way through until the other end. Look out for any fraying or tears in the cable. If there are any flaws similar to the ones mentioned, this is likely to be the problem. Replace the charger or try another available charger. Believe or not, these simple checks often fix the MacBook battery not charging issue.

MacBook battery not charging - faulty charger cable

 When you use a spare charger to test the MacBook, beware that there are a few types of MagSafe chargers for different models of Mac laptops. The output voltages are14.5V for MacBook Airs, 16.5V and 18.5V for MacBook Pro, 20V for 15" MacBook Pro with retina screen. The basic rule is that the higher-voltage (therefore higher-power) charger can replace the lower-voltage charger. 

In fact, Apple uses the same charging IC chip (ISL6259) on the logic board from 2008 to 2015 to handle different types of MagSafe chargers. This IC chip will automatically produce the right voltage to power your MacBook and charge the battery. So a higher-voltage charger will not harm your MacBook. Of course, when you buy a replacement charger, buy the same type of your original one.

Also, the MagSafe 1 and MagSafe 2 chargers are not exchangeable as the size of the connectors are slightly different. 

If your MacBook uses Magsafe charger, as long as you can the green light or orange light on the Magsafe connector, the MacBook charger is working fine.

The MacBook USB-C charger is smarter. Your MacBook will automatically negotiate a suitable voltage output (5V, 14.5V and 20V) from the USB-C charger. You don’t have to worry about the charger type, as long as the charger has the capability to power the  MacBook. 

If your MacBook uses a USB-C charger, you can buy a small USB-C power delivery tester to monitor the behaviour of the USB-C charger shown as below. It can provide information including output voltage, output current and charger temperature. If you get 14.5V from a MacBook Air USB-C charger or 20V from a MacBook Pro charger, the charger is working fine. The photo below shows the USB-C charger is delivering  power of 20.3V and 0.20A to the MacBook Pro.

MacBook battery not charging - USB-C adaptor

4.2 Check charging port and Magsafe connector

Difficulty level: Beginner

Spare part required: None

Inspect the charging port on the MacBook and the MagSafe connector for debris and burned marks. The port and the connector rely on their strong magnetic attraction to hold them together. The charging port tends to attract small metal items such as staples and paper clips. These foreign objects prevent the connector from close contact with the charging port. The connector could be very warm due to the extra resistor created by the loose contact. In an extreme case, you even can see the electric sparks. If you find burn marks on the charging port or the connector, you need to clean them or replace them as soon as possible before they cause more damages.

MacBook battery not charging - dirty MagSafe connectors

If debris is found in the charging port, you can use a toothpick or a pair of metal tweezers to get it from the port. There is no power voltage present on the four power-pins of the charging port.  The reverse-current protection gate (transistor) on the logic board prevents the battery power reverse to the port. You won’t accidentally short the circuit by using a metal tool to do the cleaning job.

Pay attention to the middle pin of the charging port. Make sure there is no film covering the pin. The SMC uses this pin to communicate with the MagSafe charger. Any thin film will block the electronic transmission, and you won’t get the green or orange light even though both your MacBook and MagSafe are working. Use a small sharp knife to clean the pins then finish up with cotton buds with 95% alcohol.

USB-C ports and plugs are also subject to dirt. You can use cotton and alcohol to clean them. Remember to remove the charger from the power outlet before you clean the connectors.

MacBook battery not charging - dirty USB-C plug & socket.JPG ATTACHMENT DETAILS MacBook battery not charging - dirty USB-C prot & plug

4.3 Reset SMC chip

Difficulty level: Beginner

Spare part required: None

The System Management Controller (SMC) controls the process of MacBook battery charging. If the SMC somehow has incorrect data of the MagSafe charger or the MacBook battery, the charger will charge the battery very slowly or even not charge at all.

Apple started to use non-removable batteries in all MacBook models from 2008. Follow these steps to reset the SMC on a MacBook with non-removable battery:

  1. Hold the power button for at least 5 seconds until the MacBook turns off.
  2. Connect the MagSafe charger, hold Shift-Control-Option on the left-hand side keyboard and the power button simultaneously for 10 seconds.
  3. Release all the keys.
  4. Press the power button to turn on your Mac. Now you have successfully reset the SMC.

Resetting the SMC on MacBooks with removable-batteries is simple.

  1. Hold the power button for at least 5 seconds until the MacBook turns off.
  2. Remove the power adaptor and the battery from the MacBook.
  3. Hold the power button key for 5 seconds to discharge any remaining electric energy in the capacitors of the SMC circuit. Alternatively, you can wait for a few minutes until the capacitors discharge naturally.
  4. Re-install the battery back to your MacBook. Now you have successfully reset the SMC.

If resetting the SMC cannot solve your MacBook won’t charge problem, reset the PRAM as discussed below.

4.4 Reset non-volatile random-access memory (NVRAM)

Difficulty level: Beginner

Spare part required: None

NVRAM contains user-defined data such as screen brightness, keyboard backlight setting and sound volume setting. If this data is corrupted, your MacBook won’t charge the battery or charge extremely slow.

To reset the NVRAM, follow these steps:

  1. Hold the power button for at least 5 seconds until the MacBook turns off.
  2. Press the power button to turn on the MacBook.
  3. As soon as you hear the chime or see any light on the screen, hold Control-Option-R-P four keys simultaneously until the MacBook restarts.
  4. Release all the four keys.
  5. After reboot, you have reset the NVRAM.
If you still have the MacBook not charging issue, move on to the next level – hardware faults troubleshooting.

4.5 Check battery connector

Difficulty level: Basic

Spare part required: None

All pre-2016 MacBooks use nine-pin connectors to connect the batteries to the logic boards. Pin 6 is used for battery detection. When you connect a battery to the logic board, this pin will send a signal to the battery internal “smart” circuit to turn on the “safety switch" called MOSFET. Therefore the electric current can flow in and flow out of the battery freely. This safety design prevents accidentally shorting the battery terminals and causing damage to the battery or even fire.  

UPLOADING 1 / 1 – MacBook battery not charging - battery connector loose.JPG ATTACHMENT DETAILS MacBook battery not charging - battery connector loose

Also, SMC uses pin 4 and 5 to communicate with the battery. As all these pins 4, 5 and 6 carry low-voltage electronic signals, any of them slightly loose contact will cause MacBook not charging.

Make sure there is no dirt or liquid on the connector and socket. Use cotton buds with at least 95% alcohol to clean the pins and reconnect the connector firmly.

4.6 Replace the faulty battery

Difficulty level: Basic

Spare part required: Battery for your MacBook model

The SMC uses a pair of data lines called SM-bus to communicate with the battery. SMC also uses current-sensing circuits to monitor the real-time current coming in or out of the battery. Based on this data, your MacBook displays the battery info in the notifications section.

MacBook battery not charging - Battery replace now

There are five battery notifications:

  1. Normal
  2. Service Battery
  3. Replace Soon
  4. Replace Now
  5. No Battery Available

Apple’s document has only defined the ”Normal” and “Service Battery” messages, leading to a lot of misunderstanding even misleading information of “Replace Soon” and “Replace Now” messages. We will clarify these messages here. 

“Normal” means your battery is fine. Your battery retains more than 80% of the original capacity. 

“Service Battery” means the battery has degraded to less than 80% of the original capacity. Usually, the battery still can last for two or three hours of normal usage. You may choose to replace the battery but it is not urgent. The battery could last for a year or two if you connect your MacBook to the charger most of the time to reduce battery usage.

“Replace Soon” means you need to arrange a battery replacement soon. Apple has not specified the criteria of this message. Our test data shows that this message means your battery retains less than about 50% of the original capacity. If you still use the battery, keep an eye on it and make sure the battery is not swollen. Below is a swollen battery in a 13" MacBook Pro. An inflated battery will put pressure on the case, touchpad and even the logic board.

MacBook battery not charging - Swollen battery

If you notice that your touchpad cracks or pops up, as shown in the photo below, you most likely have an expanded battery. You need to replace the battery immediately to prevent more damage.

MacBook battery not charging - touchpad pops up

“Replace Now” means that the SMC still can communicate with the battery, but very little or even no current can flow in or out of the battery. If you disconnect the charger, the MacBook will shut off at once. The battery finally comes to the end of its life.

“No Battery Available" with a cross mark on the battery icon as on the photo below:

MacBook battery not charging - No battery available

It means the SMC cannot communicate with the battery at all. Your battery is either completely dead or not connected to the logic board properly. Usually, replacing the battery can solve the problem. But from time to time even when you replace the battery, you still get the “No Battery Available" message. This symptom is a strong indication that your logic board is faulty. You need to get your logic board repaired to solve the MacBook not charging problem.

If your battery is faulty, you can get the battery replaced by a service provider or replace the battery yourself.  When you order the battery online, quote the battery model instead of the MacBook model to ensure you will get the right battery for your MacBook. For example, 15" A1398 MacBook Pro 2012 uses battery model A1417.

MacBook battery not charging - 15 MacBook Pro 2013 battery part number

When you replace the MacBook battery yourself, use your fingernail or a plastic stick to remove the battery connector from the logic board. Never use a metal screwdriver. Otherwise, you may short circuit the battery or even worse, destroy the SMC by sending the 12V battery power directly to it.

MacBook battery not charging - disconnect the battery

The battery is attached to the MacBook case by screws in Pre-2013 MacBook Pro and Pre-2018 MacBook Air. You simply remove the screws and disconnect the battery connector from the logic board. If you purchase replacement batteries online, most of them come with a handy screwdriver.

Apple chooses to glue the batteries to the MacBook case in 2013 onwards MacBook Pros and 2018 onwards MacBook Airs. Removing the glued battery from the MacBook case is a bit hard for beginners. Pay attention to the dedicated logic board. You don’t want to knock off some chips on the logic board and destroy it.

The battery connection in newer MacBooks with USB-C charging ports is different. The power lines and data communication lines are no longer on the same connector. Instead, the power lines (“+" and “-" terminals) are connected to the logic board secured by a T-5 screw to provide better contacts. The data lines are connected to the logic board via a flex cable.

The correct procedure to remove this type of battery is crucial. You need to remove the flex cable from the logic board first. Then use a T-5 screwdriver to remove the screw and disconnect the power terminals. Once you remove the data flex cable, the smart battery will turn off the “safety switch" inside the battery and there will be no power on the power terminals.

If the data flex cable is not working due to loose contact or liquid damage, you will get the “No Battery Available" message.

IT-Tech Online is a leading Mac repair specialist in Australia. We are more than happy to help you if you cannot fix the problems yourself. We offer competitive prices for MacBook battery replacement. Please contact us. Our experienced staff will call you to assess your situation and provide a free quote for you.

4.7 Check battery indicator circuit

Difficulty level: Basic

Spare part required: None

The pre-2013 MacBook Pro comes with a battery status indicator. You can push the button to see how much percentage the battery retains the power. This indicator shares the same circuit with which the SMC uses to communicate with the battery. If the indicator is faulty, especially after being exposed to water, the SMC cannot talk to the battery, therefore reports no battery found.

MacBook battery not charging - faulty battery indicator light

Fixing this problem is easy. You can replace the indicator, or simply unplug the indicator cable if you decide not to use the indicator function any more.

4.8 Check faulty DC-in Board

Difficulty level: Intermediate 

Spare part:  MacBook Pro DC-in board 

The battery on MacBook Pro not charging could be caused by a failed DC-IN board in the Pre 2013 Mac. The SMC uses the middle pin (pin 3) to talk to the MagSafe charger. There is a diode on the  DC-IN board connecting pin 3 to the ground to protect the SMC circuit.

MacBook battery not charging - faulty diode on DC board

If there is a higher voltage accidentally applied to pin 3, for example, power surge or pin 2 (16.5V – 18.5V) shorted to pin 3, the diode will short this high voltage to the ground to prevent the dedicated SMC being damaged. 

If the diode has been damaged, the SMC cannot talk to the MagSafe charger so you won’t get the green light. Of course, your MacBook won’t charge the battery as there is no power coming from the charger.

Fixing the problem is easy. You can buy a DC board online for a few dollars. Depending on the MacBook model, you may need to remove the logic board to disconnect the DC board cable. 

If you need to remove the logic board, pay attention to the fan connector. The fan connector is very easy to peel off. Repairing the fan connector requires micro-soldering skill and adds extra cost to your repair bill. 

You even can remove the diode, and the DC board will work again. But bear in mind that there is no protection to your SMC circuit in case a power surge occurs.

4.9 Replace faulty I/O board cable

Difficulty level: Intermediate

Spare part:  MacBook I/O board cable

There is a cable connecting the logic board to the I/O board. The SMC uses the “one-wired” circuit to talk to the MagSafe charger. This “one-wired” signal needs to pass the cable to the I/O board and finally reaches the charger.

MacBook battery not charging - cable loose

If the cable is loose, the “one-wired” signal will not pass to the charger so you won’t get the green light on the charger connector and your MacBook won’t charge the battery.

Remove the cable,  clean the cable and two connectors on the logic board and the I/O board with a toothbrush and  95% alcohol. Remember the cable direction. If you connect the cable reserved, you may damage the MacBook. 

The cable is prone to liquid damage. If you spill water on your MacBook Air right before you get the MacBook not charging issue, you most likely have a corroded cable and (or) connectors. 

You can get the I/O board cable for a few dollars online. If your I/O board is faulty, you also can get it for less than fifty bucks.

4.10 Repair the faulty reverse-protection circuit

Difficulty level: Advanced

Equipment required: Hot air gun rework station

If you connect an Apple original MagSafe charger to the MacBook, you can’t see any green or orange light on the connector. But if you plug in a third-party charger to the MacBook, you can see the green or orange light and your MacBook battery is charging the battery perfectly. This unique symptom indicates that you have a faulty reverse-protection circuit on the logic board.

The reverse-current protection circuit is designed to prevent the internal battery power “reverse" out from the battery to the charger. If the reverse-current protection circuit has current leakage, even as little as a few milliamps, the original MagSafe charger will detect the leakage, therefore, shut off the output. 

On the other hand, the third-party charger has no leakage detection function; therefore, continue to output as usual. 

Now you have two options. You can keep using the third-party charger as the leakage does not affect the performance of your MacBook. The second option is to replace the reverse-current protection MOSFET. You need a hot air gun rework station to perform the task.

MacBook battery not charging - faulty reverse current protection transistor

5. Understand the principle of MacBook battery charging circuit

We are going to look at some case studies at expert-level.  Fully understanding the principle of the MacBook charging circuit is the key to success. Here we take  MacBook Pro schematics 820-4924A for study.

File name : MacBook-Pro-2015-Battery-connector.pdf

File name : MacBook-Pro-2015-Charging-circuit.pdf

  1. When a battery is connected to the logic board, a 10KΩ resistor R7050 is connected to the battery connector J7050 pin 15. The smart battery internal circuit detects the presence of the 10KΩ resistor, then opens the battery internal MOSFET to output the battery voltage. In other words, the battery output will remain close unless a 10KΩ resistor is detected. This is the safety feature of the smart battery.
  2. The battery voltage PPVBAT_G3H_CONN is about 10-12.6V depending on whether the battery is fully charged or not. PPVBAT_G3H_CONN passes the internal diode of Q7155, charging current sensing resistor R7150, fuse F7140 and becomes PPBUS_G3H power rail.
  3. Now we have the PPBUS_G3H power rail. Bear in mind that this voltage is passed from the diode inside the MOSFET Q7155. Q7155 is not open yet. So at this moment, this temperate PPBUS_G3H is a “weak” power rail and only can provide a very small amount of current. This is a great safety feature of Apple logic board design. It prevents the battery from exposing due to overheating if there is a short on the logic board. This temperate power rail is powerful enough to power a PMIC to create an always-on power rail PP3V42_G3H.
  4. The PP3V42_G3H power rail will power the System Management Controller (SMC) and power management IC U7100. SMC will read the code stored in the chip inside the battery via a pair of SMBus: SMBUS_BATT_SCL and SMBUS_BATT_SDA. This code contains information such as battery voltage, charging status, battery capacity, charging circle counts, temperature and so on.
  5. If the battery check is ok and it has enough power to power the system, SMC will communicate with the charging PMIC U7100 via a pair of SMBUS: SMBUS SMBUS_CHGR_SCL and SMBUS_CHGR_SDA. Then U7100 will output CHGR_BGATE to open MOSFET Q7155. Now we have a stable, “full power” PPBUS_G3H power rail ready for use by the laptop.
  6. When we press the power button on the keyboard, the SMC will power up the Apple laptop using the battery along.
  7. When a power adaptor is connected to the MacBook, U7100 will create its own PPBUS_G3H from the power adaptor. U7100 outputs CHGR_BGATE to control the Q7155 to achieve battery charging or discharging according to the battery status and the applications we are running on the laptop. All these functions are governed by the SMC.

6. Advanced MacBook repair (battery not charging) - case study

Difficulty level: Expert

Equipment required: Hot air gun rework station, multimeter

This is a 13” MacBook Pro 2015 with retina screen. The laptop works fine when a  charger is connected but shuts down immediately when the charge is removed. A “service battery” message is displayed on the notification section and there is an orange light on the charger connector. The customer said the laptop battery had been replaced by another computer shop but the laptop is still not charging. Initial inspection shows no evidence of water damage or corrosion.

Connect the MacBook to our metered power supply. The current drawn from the power supply is 0.027A in standby mode. Replace the battery with a known working battery. The current drawn is still 0.027A. This confirms that the problem is in the logic board. How do we fix it?

We remove the logic board from the case and inspect it under a microscope. There is no evidence of liquid damaged at all. The schematics for this MacBook Pro is 820-4924A.

  1. Measure battery connector J7050. The figures of pin 13 and 14  SMBUS clock line and data line are 0.508 and 0.509 respectively in diode mode. It means the battery communication bus to SMC should be fine. Measure pin 15 battery detection SYS_DETECT_L. The figure is 9.8 KΩ. It matches the R7050 figure on the schematics. So the battery detection circuit should also be fine.
  2. Inspect U7100 charging circuit PMIC (Power Management Integrated Circuit). There are no burned marks or burned components. Measure the value of the resistors between U7100 pin 27 and 28 CHGR_CSI_R. The figure is 22Ω, ok. Measure the value of the resistors between pin 17 and 18  CHGR_CSO. The figure is 2.9Ω, ok. The charging circuit seems ok.
  3. Measure Q7155  MOSFET in diode mode. Pin 5 to 3 is 0.472, ok. Pin 3 to 5 is an open line, very good. Both pin 5 and pin 3 to pin 1 are all open line, excellent. All these measurements indicate the Q7155 is working fine.
  4. There is no obvious faulty component found. This logic board is not easy to fix. We have to rely on intelligent guesses based on past experience – the “try and error" approach.  The U7100 (charging circuit power management IC) is the first suspect. Let’s replace it. The battery is still not charging after replacing U7100. We have just killed an innocent charging chip.
  5. The second suspect is Q7155. This MOSFET is used to control the battery charging current. Let’s replace it. The problem remains after replacing Q7155. We have just killed another innocent chip. This guess-by-experience method does not work in this case, obviously.  We have to stop this problem-solving approach before the repair job turns into a nightmare.
  6. It is time to rethink our strategies. It is hard to get the charging circuit to charge the battery in this case, but we may work the other way around. We may use a good battery alone to power the laptop without connecting to the power adaptor, so we can follow the battery discharging current flow to pinpoint the faulty components. Let’s do it.
  7. Connect the logic board to a good working order battery and measure the voltage of Q7155. The voltage on pin 5 and pin 3 drops from 12.4V to 0V and keeps repeating. The voltage on pin 4 drops from 5.2V to 0V and repeats in a circle. There is no shorted circuit on pin 5, pin 3 and pin 4. This measurement result confirms that the Q7155 MOSFET is working perfectly. For some reason, it opens for 1 or 2 seconds then closes.  It is why the voltage rises up to12.4V then drops to 0V repeatedly. We have found the problem now, but why did the Q7155 not remain open?
  8. Q7155 pin 5 connects to the battery positive terminal directly. Dropping voltage in pin 5 means the battery is cutting the output voltage by itself. If the battery is good, and there are no short circuits on the load side, then the only thing that can make the battery shut off by itself is the battery detection circuit. This circuit is very simple, consisting of only one 10KΩ resistor R7050.
  9. We measured this resistor R7050 an hour ago and the figure was 9.8KΩ. Let’s measure it again even though it still looks good with no sign of damage. This time the figure is 5.9KΩ. This resistor has an intermittent fault! This intermittent fault made us waste one hour and kill two innocent chips. If the resistor remains at 5.9KΩ all the time, we could have fixed the problem in five minutes. The intermittent faults are the most difficult faults to deal with.
  10. Replace R7050 with a good 10KΩ resistor and we get a working laptop.

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