Charging a sealed lead-acid battery

Battery manufacturers recommend charging 12V lead-acid batteries at a charge voltage of 13.5 - 13.8V for standby, and 14.4 v - 15v for cyclic use(charging and discharging) - but if using the latter, which gives a faster charge, you must turn it off when fully charged. I use the 13.8V option, and leave my battery charging until I need it - although it's always fully charged after about 12H. The charger uses a LM317 adjustable regulator. This is an adjustable 3 terminal positive voltage regulator capable of supplying in excess of 1.5 amps over an output range of 1.25 to 37 volts. The device also has built in current limiting and thermal shutdown which makes it essentially blow-out proof. A 6 - 0 - 6V (or 12V) 6VA transformer feeds a bridge rectifier, and the signal is smoothed with a capacitor of 4700uF at any voltage above 16V. This gives about 17.5V to the regulator. The output voltage is set to 13.75V by the two resistors. Only 6 components, it can be built as a birds nest on the transformer, or as I have on a little bit of veroboard. The 1A regulator doesn't need a heat sink. All parts available from Maplin's.