Fourteen volts is a good number for a fully charged battery that is ready to be connected to an inverter. Learn how to connect an inverter for a solar power system from a professional in this free energy conservation video. Expert: Roger Bacon Bio: Roger Bacon is the owner of RGB Home Repair and Renovation in Santa Barbara California. He has experience in all phases of home repair and renovations such as plumbing, heating and solar power. Filmmaker: Diana Bacon