BATTERY CHARGING SYSTEM FOR THE SP.500 In a previous issue we featured a trickle charging unit for the SP.500 which had been ... Its life is thereby very much prolonged and as it is permanently in circuit the risk of faulty terminal connections is eliminated. ... 6A at 12V and with two accumulators, one, 72 amp. hr. for the tungsten lamp (TL) and the other, 10 amp. hr., for the photocell amplifier (PA).