I have an Inspiron 5567. It’s 1yrs old and the battery shows ~27WH remaining capacity from 42WH (original). The problem is...

You don’t get the problem I think. Let me describe it again. The cells are fine. If the reported capacity and the real capacity would be the same (27WH) there’s no way the laptop with it’s original charger can put 10 more WH into the battery and the battery can hold that extra charge. I know that Li-ion batteries lose capacity over time/charge cyle. But you shoud see clear how Li-ion BMS/protection/SoC(state of charge) approximation works. It’s use a method called coulomb counting. The idea of CC is to count the electrical charge coming from /going to the cells. It’s integrating the current between the battery and the load. The BMS(battery management system) measures and calculates everything. The problem is self discharge and losses inside the battery. The CC method use full capacity and the integrated charge, subtracts them and gives the result as the SoC. But the integrated value can drift from time to time because of the losses and self discharge. On Lenovo batteries it’s not a problem. If you do a...