I have an old friction drive, dual motor Zap unit that still works, I think. However, I'm thinking about bringing it out of retirement. It used a 12v 20ah SLA battery which I'd like to replace with a newer, lighter type of battery. What type of replacement battery and charger would substitute for the original Zap battery? No, I don't want to spend a fortune on a 12v system, but I'm willing to play with a few hundred dollars for this project.