The BTL fast NiCad battery charger incorporates microprocessor controlled electronics to ensure stand by batteries are always in a good state of charge. The charger runs off a standard 220V 50Hz supply and is capable of re-charging a fully discharged battery in 6 hours. Under normal conditions the batteries are trickle charged to maintain full capacity. After a power failure the charger switches to boost charge to restore the batteries in the minimum time. The mains voltage, the charger state and batteriy terminal voltage are constatnly monitored to determine the operating conditions. A manual override is provided so that a boost charge can be aplied and a thermal trip can be used for additional protection if required.