Firstly, we need to know there is 2 parts of Battery.
1) The protection circuit.
2) The battery cell.
1) The protection circuit is provide to protect the battery cell for charging and dis-charinge.
Regarding to OEM standard. (Original battery from big brand like, Nokia, Motorola,..) It must have 2 protection.
Over-charging protection to protect the cell that can stop charging when the battery is full charge. Otherwise, it will over-charge become overheat and have explosiion danger. However, most of the charger and mobile phone itself have over-charge protection as well. That's mean it is always have 3 protection during charging. Mobile Phone, charger and the battery itself.
Over-discharge protection to protect the cell for over-discharge. When there is a large current draw out from the battery, the circuit will cutout the battery. Just like a fuse in our home. Therefore, when it is short-circult and it will cut out the supply. Otherwise, it will over-heat in a few second and have explosiion danger. It is quite often you know have phone explosion during use because of the battery do NOT have this protection. But in gerenal if the phone is in good condition, this is no problem to use. Just in case the phone got the problem and make short circuit inside.
2) Battery cell.
In past years ago. Most of the battery cell are made in Japan and very expensive. Nowadays, most of China brand battery cell are very famous like, BYD, BAK, etc.. They are also OEM to original battery for Motorola and Nokia.
In the market have different Grade of Battery. Most supplier always say they are A Grade Battery.