The main Types of Rechargeable Batteries are NiCd - Lead Acid - NiMH - Lithium ion. The Gel Lead Acid Battery is Termed Maintenance Free and may have to be treated differently for charging.
List of battery sizes - Wikipedia
4.5 Volt - D - C - AA - AAA - 9 Volt - SR41/AG3 - SR44/AG13
Battery Charger Circuits and Resources
Solar charger for lead-acid batteries
The charger will stop charging once a pre-set voltage (temperature compensated) has been reached, and recommence charging when the voltage has dropped off sufficiently.
12 Volt Gel Cell Charger
When a discharged gel cell is connected, the charger goes into a fast charge mode at a fixed rate of 400 ma. After the chip detects the voltage leveling off or when 4 1/2 hours has elapsed.
Temperature Controlled NiCd Charger
This circuit is for a temperature controlled constant current battery charger. It works with NICD, NIMH, and other rechargeable cells.
Battery charger 150-1700 mAh with PIC16F876
This is the extension of the simple battery charger to different battery capacities. The software and the controller are largely identical.
MAX846A Cost-Saving, Multichemistry, Battery Charge Chip
In its simplest application, the MAX846A is a stand-alone, current-limited float voltage source that charges Li-Ion cells. It can also be paired up with a low-cost microcontroller (µC) to build a universal charger capable of charging Li-Ion, NiMH, and NiCd cells.
Rechargeable Batteries and Chargers
There are three types of rechargeable batteries. They are Nickel-Cadmium (NiCd), which are the oldest type; Nickel-Metal Hydride (NiMH), which were developed around the same time that low-cost digital cameras were invented.