Abstract: A battery charging system is disclosed wherein there is control means connected with a battery charger responsive to the temperature of a temperature sensor connected with a battery to sense its temperature whereby to switch off the charging when the battery temperature is at or above a predetermined temperature unsuitable for charging. The control means includes a signal transmitter and a signal receiver. The signal transmitter applies a pulsed signal to the charging leads when the temperature of the battery is at or above the predetermined temperature and the receiver detects this and switches off the charging. A signal transmitter and temperature sensor, and a battery fitted therewith is also disclosed.