12V Battery Charger

This circuit is a high-performance charger for gelled-electrolyte lead-acid batteries. This charger quickly recharges the battery and shuts off at full charge. Initially, charging current is limited to 2 A. As the battery voltage rises, current to the battery decreases, and when the current has decreased to 150 mA,  the charger switches to a lower float voltage, which prevents overcharge.

12V Battery Charger Circuit Diagram:

When the start switch is pushed,  the output of the charger goes to 14.5 V. As the battery approaches full charge, the charging current  decreases and the output voltage is reduced from 14.5 V to about 12.5 V, terminating the charging. Transistor Q 1 then lights the LED as a visual indication of full charge.