NiMH batteries have a memory effect, but they are small. The memory effect is not obvious, it means that it can be charged multiple times, even when it is used up without much influence. Therefore, when using a nickel-hydrogen battery, it can generally be charged directly without considering discharge. Nickel-metal hydride rechargeable batteries can effectively relieve memory effects by discharging them once every three months. If a battery is not fully discharged this time, in the subsequent charge and discharge cycle, the power that is not released in this part can no longer be released. This is the memory effect of the battery.
Memory effects generally only occur in nickel-cadmium batteries, nickel-hydrogen batteries are less, and lithium batteries do not. The reason for this is due to incomplete partial charging and discharging of the battery. This will reduce the temporary capacity of the battery, resulting in a shorter use time. Low-voltage nickel-metal hydride batteries have no memory effect. High-voltage nickel-metal hydride batteries have the same "memory effect" as nickel-cadmium batteries. Lithium-ion batteries do not have a memory effect.