Modern acid batteries and lead plates, are embodiment of simplicity in use. Unlike NiCd batteries, they must be recharged by connecting to a constant voltage. In this situation, the loading current will provide a good indication of the state of loading.
These batteries can be quickly loaded as long as the loading current is limited even at the beginning of the trial proceedings. The charger which we propose it has a voltage regulator, IC1, and a variable current limiter which consists of T1, R1 and R4. Once the current through R1 becomes too large, T1 is opening and the output voltage decreases.
Values, in volts, of output voltage is given by the formula:
1.2 (P1 + R2 + R3) / R3
For a 6V battery, the required load voltage for a rapid loading will be 3 x 2.45 = 7.35V. In this case, the actual total value for R2 + P1 will have to be 585 Ω.
To charge 12V batteries, the amount needed for R2 + P1 should be around 1290 Ω. Voltage at the entrance must be at least 3V larger than that of output.
LM317 integrated circuit needs heatsink, not only for that, otherwise, can easily destroy, but also because, at high temperatures, it can not provide the current maximum output.