Now days there are several battery options. NiMH (AKA Nickel – Metal Hydride) is a pretty good choice if the tool you are looking at has it available as an option. This type of battery has many positive features with out the hi-cost of the Li-Ion. Since NiCd will be the next battery type to go extinct in the cordless power tool world, we would suggest staying way from them, unless of course you get some crazy awesome deal that you can’t pass up. If performance, weight and charge time are main considerations the Li-Ion is the best choice hands down.