BamaBuzz4UA

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 would me greatly appreciated