Free circuit schematics - wiparat.com

A flyback converter implements a current-limited power supply to charge lead-acid batteries. The MAX773 current-mode controller limits the output current and the flyback transformer provides isolation and flexibility for input voltages both above and below the battery voltage. The MAX471 current-sense amplifier monitors the charging current and feeds back to a threshold detector so that [...]

The above circuit will charge any 2-cell * Li-Ion battery pack. Maximum current is about 650 milliamps. The circuit is designed for batteries of 900mah or higher. Note this circuit is NOT for Li-Metal batts (i.e. Duralites). Power source can be a 12v Gell cell (Power panel), or can be powered by a car’s cigarette [...]

The charger in this project is designed to charge two AA NiMH or NiCd cells of any capacity (as long as they are the same) at about 470mA. It will charge 700mAh NiCds in about 1.5 hours, 1500mAh NiMHs in about 3.5 hours, and 2500mAh NiMHs in about 5.5 hours. [...] Link