The MH-C490F Stealth Two-Hour Compact 4-Bank 9V NiMH Battery Charger from Powerex is a small charger for 1-4 7.2V, 8.4V or 9.6V NiMH rechargeable batteries. It has a Delta-V based microprocessor, which charges batteries to their full potential. The microprocessor automatically switches from rapid charge to trickle charge after the batteries are fully charged to ensure that they maintain their total capacity. Additionally, FLEX pulse charging conditions and enhances battery performance during charging. The MH-C490F charges batteries in 120-160 minutes--so you don't need to wait overnight for a full charge. Rejuvenate your batteries quickly when you're on-the-go--even in the car (requires optional car kit, sold separately). The Powerex Precharged Rechargeable 9V Battery has a voltage of 9V and a capacity of 230mAh, with a minimum capacity of 215mAh. The battery is capable of being stored for an extended period of time and still retaining a full or nearly full charge. After a year, for instance, it will retain up to 85% of its capacity. This product comes pre-charged and can be recharged up to hundreds of times. The purchase of NiMH batteries like this saves you money, since you won't need to buy endless supplies of non-rechargeable alkaline batteries.