Power supply apparatus

Power supply for supplying a direct voltage load (2) and comprising a rechargeable battery (4), and a voltage generator (6) for recharging the battery (4) and supplying power to the load (2), including first control means (20,16) to control supply of current from the voltage generator (6) to the load (2) and for preventing reverse flow of current, and second control means (21) to control supply of current from the voltage generator (6) through the first control means (20,16) to the battery (4) and from the battery to the load (2). The control means (20,16;21) present selectively a high impedance state (23), a low impedance state (26) or a controlled impedance state (29,32).