Repair iPhone 6 Plus battery percentage inaccurate and grey screen error

Trouble Phenomenon

The iPhone 6 Plus battery percent inaccurate, and often reboot.

Repair process

First test the charging function, it shows normal, but the battery power percentage jump frequently. Base on repair experience, this phenomenon should be a reboot frequently caused by battery failure, so we should repair the battery power percentage inaccurate first.


Connect iPhone to i4 tool, the position of battery information shows no data, this failure is the CPU doesn’t recognize the battery, so i4 tool can’t read the battery data. As shown in picture 4-5-1.


The main reasons for not recognizing battery information as follows:

  1. The battery is damaged
  2. The circuit from middle pin BATTERY-SWI of battery interface J2523 to F2 of charging chip U1401 is broken and the U1401 was damaged
  3. The problem of circuit from U1401 G1 # to CPU AG4 # and problem with the CPU itself.


The schematic diagram is shown in picture 4-5-2


Replace the new battery and test it, i4 tool still can’t read the battery information. Then measure the diode data of battery middle pin with Multimeter, the diode data is 380 which is normal, so the line from battery to U1401 is normal. Next we remove the U1401 IC, and then measure the line from G1 pin to SWI of CPU, the diode data of G1 is 450, its normal. Now, we can judge U1401 or CPU is damaged.


After replace the U1401, it still can’t read the battery. This fault is not caused by the CPU welding, but because the CPU damage pulls down the voltage of the SWI line, so we can increase the SWI voltage by connecting the resistor externally.


Connect a 2.2K resistor on PP3V0_TRISTAT, the other end of the resistor is attached to U1401 G1 pin (also can connect to middle pin of battery). The picture of solder jump wire is shown in 4-5-4.


After soldering jump wire, the picture is shown in 4-5-5


Finally, turn on iPhone 6 Plus and connect to i4 tool, now it can read the battery information, the fault has been repaired. As shown in picture 4-5-6.


Tips: you can use 3U tool to replace the i4 tool.


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