Trickle charging or float charging, means charging a battery at a similar rate as to its self-discharging, thus maintaining a full capacity battery. Most rechargeable batteries, particularly nickel-cadmium batteries or nickel metal hydride batteries have a moderate rate of self-discharge, meaning they gradually lose their charge even if they are not used in a device. Care must be taken, however, that if a battery regulator is not employed, the charge rate is not greater than the level of self-discharge, or overcharging and possible damage or leakage may occur.

Thermoelectric generators may be used as a power source for charging batteries depending of the load requirements of the application and stability of the heat source.