zlacker

I remember replacement PSP batteries being similar. It was basically impossible to find third party batteries that were as good as OEM ones, even the ones that advertised higher mah numbers than the stock Sony ones were awful (despite even being physically bigger).

>>p1neco+(OP)
Maybe the charger charges differently and with a larger safety margin at 100%[1] when it detects a non-EOM battery?

[1] 100% doesn't mean that the battery is fully charged, it means that the detected level is what the charger is prepared to go to. To conserve battery life it is not uncommon to have a 100% indicator when the battery is only 90% charged, and a 10% indicator when the battery is only 20% charged.