Can car batteries power a house?
A car starting battery is designed for short engine-starting bursts, so it is not a household backup system by itself. A home battery system must match the loads, inverter, battery chemistry, charging equipment and installation requirements.
How many amp-hours is 5,000 watt-hours?
Use amp-hours = watt-hours ÷ nominal battery-bank voltage. For example, 5,000 Wh ÷ 12 V = about 417 Ah at 12 V under an ideal calculation. It is not 50 Ah. If a 1,000 W appliance runs for five hours, it uses 5,000 Wh of energy at the appliance; an inverter and battery bank must supply more than that on the DC side because conversion is not lossless.
This arithmetic does not give a safe battery count. Real capacity depends on system voltage, usable capacity allowed by the battery maker, inverter efficiency, startup surge, other loads and the required backup time. Size a purpose-built system from the equipment specifications and have a qualified installer check the design.
Sources: U.S. Energy Information Administration: Batteries, Circuits, and Transformers
