How to activate NiMH batteries

There are two types of NiMH battery activation: one is new battery capacity activation, and the other is old battery internal resistance activation.

There are many discussions on the activation of new batteries. First of all, it should be clear that the purpose of new battery activation is to stimulate battery activity by activating the active factors in the battery. The reason is that the self-discharge of NiMH batteries is large, and the power will gradually be lost during long-term transfer, thereby reducing the battery activity and entering a dormant state. If several complete charges and discharges are not performed, the output capacity will not reach the nominal capacity due to the memory effect of NiMH batteries. In specific practices, three complete charges and discharges are usually performed, among which the charging mode is preferably 0.1C. This is because when the battery is not activated and has a small amount of power, high current charging will cause damage to the electrode. In theory, when charging for the first time, if the battery has a power of more than 40%, it can be used first and then charged. On the contrary, if it is less than 40%, it should be charged first and then used. In practical applications, new batteries have instructions for use and can be operated according to the manufacturer's instructions. It may take at least three complete charges and discharges to fully meet the capacity standard, and some are required to be as long as 5 times, because the available power after the first charge may be only 1/3 of the nominal capacity.

After long-term use, the capacity of old NiMH batteries will decrease. At the same time, the internal electrode will produce an oxide layer, which will increase the internal resistance of the battery. The decrease in capacity is irreversible. Therefore, reducing the internal resistance of the battery is the key to activating old NiMH batteries. Otherwise, old NiMH batteries will become less and less adaptable to large-current electrical appliances. NiMH batteries with increased internal resistance can be activated by discharging with a large current. In practice, short-circuit tests are usually performed. In a short circuit, the current will increase from small to large, and the NiMH battery will slowly heat up. When the battery body reaches 40°C, the discharge will stop. When the temperature returns to normal, the short-circuit discharge will be performed again. After this cycle, the short-circuit discharge process will be completed until the battery voltage drops to 1.0V. Some NiMH batteries with low internal resistance may be able to be used normally after one discharge, so there is no need for a cyclic short circuit.

Precautions The purpose of activating new and old NiMH batteries is different. Therefore, the short-circuit test must not be used to activate new batteries.