I recycle old computer battery backups into inverters for my vehicles. I generally use the APC smart-ups line of battery backups for my computers. When I have an extra one of the 700 to 1000 volt amp units with a bad battery, it can become an inverter. Most of the APC units of this size use a single 12v battery, 2 6v batteries in series, or 2 12v batteries in parallel. I just remove the APC battery and connect to the cables inside the APC. I also remove the warning buzzer from the circuit board inside the battery backup so it doesn't beep at me for not supplying it with 110v power. This gives me a stable, clean, pure sine wave inverter for almost no cost.