I would advise you to buy the Victron Phoenix Inverter Compact 1200VA – 2000VA. The Phoenix Inverter Compact is a pure sine wave inverter with high efficiency. It is developed for professional duty and is suitable for a wide range of applications. Victron is regarded as one of the US's best. Your monthly utility bill is based on the number of kilowatt-hours of power drawn from the power grid. The typical US household uses 30kWh of power per day to satisfy the power demand. The bulk of the 30kWh is consumed during the 4 pm to 8 pm peak usage. A 12V 100Ah battery can store and deliver 600Wh if it is a lead-acid type battery (50% of 1,200W) and 1,200Wh if it is a Lithium-Iron-Phosphate type battery. Assume you want to run a 120W computer for a minimum of five hours per day. You would need to draw 120W.