The universal battery charger’s output voltage is adjustable and regulated, and has an ajustable constant-current charging circut that makes it easy to use to use with most NiCad batteries. The charger can charge a single cell or a number of series-connected cells up to a maximum of 18V.

This 12V battery charger 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 2A. As the battery voltage rises, current to the battery decreases, and when the current has decreased to 150mA, the charger switches to a lower float voltage, which prevents overcharge. When the start switch is pushed the output of the charger goes to 14.5V.

Cell phone battery charger circuit presented here comes as a low-cost alternative to charge mobile telephones/battery packs with a rating of 7.2 volts, such as Nokia 6110/6150.
The 220-240V AC mains supply is downconverted to 9V AC by transformer X1. The transformer output is rectified by diodes D1 through D4 wired in bridge SANI THEO configuration and the positive DC supply is directly connected to the charger’s output contact, while the negative terminal is connected through current limiting resistor R2.