Power and energy answer different questions
Power, measured in kilowatts (kW), describes the rate of energy transfer. Energy, measured in kilowatt-hours (kWh), describes an amount of energy. The battery energy rating and the continuous power capability are separate specification items.
Start with the load
A constant 2 kW load running for 3 hours uses 6 kWh at the load in an ideal calculation. This is an illustration, not a recommendation for a 6 kWh battery. The chosen battery must account for usable depth of discharge, conversion losses, reserve and the operating conditions.
Check peak demand separately
A load can have an average power requirement that is much lower than its starting or peak demand. The battery, inverter, cables and protection must be considered as a system. Enough stored energy does not automatically mean enough instantaneous power.
Distinguish nominal and usable energy
Nominal energy and usable energy may differ because of operating limits and reserve settings. A simple nominal estimate is voltage multiplied by amp-hours, divided by 1,000 to express kilowatt-hours. Real usable energy depends on the battery and operating conditions.
Build a project-specific specification
Share the load profile, daily energy use, backup requirement, inverter details and expected environment. The result should specify both energy and power, with the relevant operating conditions. This guide supports an engineering discussion and is not an installation design.
Examples explain general principles. They do not establish the specification or performance of a particular evjrich product. Final selection requires the application and equipment details.