NiMH battery chargers cannot safely charge lithium batteries for the following main reasons:
1. Voltage and charging mechanism differences
The nominal voltage of a single NiMH battery is 1.2V, while the nominal voltage of a lithium battery (such as ternary materials) is 3.7V. The actual operating ranges are 2.8-4.2V (lithium battery) and 1.0-1.5V (NiMH), respectively. Voltage mismatch will cause abnormal charging.
Lithium battery charging requires constant current and then constant voltage, but NiMH batteries do not have this process. Direct use of NiMH chargers may cause lithium batteries to overcharge or fail to be fully charged.
2. Safety risks
NiMH chargers lack the voltage monitoring and overcharge protection functions required by lithium batteries, which may cause lithium batteries to overheat, swell ("charge pregnancy"), and even cause combustion or explosion.
Lithium batteries are sensitive to charging current. High-rate charging (such as above 1C) requires a dedicated charger, while NiMH chargers usually only support currents below 0.2C and cannot adapt to the needs of lithium batteries.
3. Exception: Smart multi-function charger
Some multi-function balance chargers support compatibility with two types of batteries through parameter settings, but the voltage, current and other parameters need to be adjusted manually, and the device needs to be equipped with a balanced charging function (such as a BMS system).
