This cheap and easy to build NiCd/NiMH Battery Charger is suitable for automatically charging a wide range of batteries for many applications. Proper chargers are usually expensive and cheap chargers supplied with the original equipment often incorrectly charge the cells and dramatically shorten their life. This ‘intelligent’ charger was designed for high current and rapid charge applications such as cordless power tools and model racing cars.source

This design is a 3A battery charger intended for use with 5-cell Ni-Cd or Ni-MH battery packs (but can be modified to suit other numbers of cells). The circuit includes automatic shutoff that occurs when the battery temperature rises 10°C above ambient.This battery charger was developed specifically for applications using either Nickel-Cadmium (Ni-Cd) or Nickel-Metal Hydride (Ni-MH) batteries that will accept a 3A fast-charge rate, and provides automatic shutoff of the high-current charge when the battery is full.The circuit use LM2576.source

This is a fast-charges 500-mAhr circuit for AA Ni-Cd cells. The number of cells can select by two switch, the circuit handles two to eight of AA Ni-Cd cells,The input voltage must be at least 15V. Charging starts when you plug in the battery.There is LED to indicate when the battery is fully , and the charger switches to trickle-charge mode.source

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. The charger incorporates an automatic charge cut-off circuit based on cell temperature, and the cells can be left in the charger indefinitely after cut-off. source

This is the reverse engineered circuit diagram from a popular mass produced solar light. The light automatically turns on when there is no light falling upon the solar cell(like a light sensor switch), so the parts count is minimal. The charging circiut is not particularly efficient since the battery must charge through a plain diode. source