NM-C741 Lenovo L14 no battery detected

[raed8383]

There's a problem with customer laptop and I don't have time to check it. I need advice if possible. The laptop owner is in a hurry.
Laptop model: Lenovo Thinkpad L14
NM-C741
The problem is that it reads 100% full charge, but when I disconnect the charger, the laptop power disconnects immediately. It's either there's no battery or the laptop doesn't detect it. I know that more than one battery has been replaced due to possible compatibility issues, so I hope you can help me quickly.

[mon2]

Attach the battery only. Carefully measure the voltage to ground on each pin of the battery connector.

Post each measurement.

[mcplslg123]

Very likely either the SDA or SCL line is broken.

[raed8383]

mon2

Attach the battery only. Carefully measure the voltage to ground on each pin of the battery connector.

Post each measurement.

THISI IS WITH CHARGER >>> ONLY BATTERY NO VOLTS

1- 1.048V
2- 1.049V
3- 3.2V
4- 3.2V
5- 0.122V
6- 0.00 V
7- GND
8- GND

[mon2]

The pins 3&4 are ok and not shorted. These are the SMBUS lines used by the EC to communicate with the battery pack.

Remove all power. Meter in resistance mode. As per post #3, test the point-to-point resistance from this battery connector back to the EC. Testing the resistance to check if there is a break in the SCL / SDA lines from the SMBUS master (EC) and the SMBUS slave (battery pack).

If you have a low cost bus analyzer or oscilloscope, you can also test the SCL and the SDA lines for activity. In the absence of a proper response, the SDA line for example (assumed to be broken) will return '1' = FFh = full battery assumed from this bit pattern. That is, the SDA line is parked in the '1' state so the host motherboard is incorrectly reading a 'full charge' status.

Review each connection of the SDA line from the EC to the battery pack connector. Then repeat for the SCL line. Assuming that the battery connector, contacts, battery is ok then the pcb traces and parts in the path are the suspects.


Pins:

69
70

on EC are the SMBUS bus master pins for the charger IC and the battery pack under review. Test if these connections reach the charger IC and also the battery pack.