Charging Circuit Schematic

I am building charging system for 12v tool batters ( drills, lights, etc. ). I found a 12v a/c adapter and I cut the end off the but bullet connectors that hook up to a wire with a shielded female spade connector. The shade fits the 12v battery. My question is - is there a way to design a circuit that will let me know when its charged, like with a red and green light. Any help or schematic whould me greatly appreciated.

Tool batteries might use one of four different kinds of cells, Lead-Acid, Nickel-Cadmium, Nickel-Metal-Hydride, or Li-Ion. The most common is Nickel Cadmium, but the newest ones are using Li-Ion. In any case, each type of battery must be charged in a different way, and some of them are not simple. For this reason, a special charging controller IC is usually used to make a charger, and it is this IC that usually also has LED outputs to indicate what is going on. Here is more detail:

Batteries in a Portable World. A handbook on rechargeable batteries for non-engineers

Thank you for that info. I would have never found that site and it is what I was looking for. All the info I need is right there.