What does a home battery actually back up?

A good backup conversation starts with a list, not a product name. Write down what you want available during an outage, which items can wait, and how long you would like to cover.

Make three lists.

First, list your daily essentials. Then add the larger loads you would like to consider. Finally, list what you can postpone. Those lists become a brief for the person designing the system; they are not proof that one battery can run everything.

Ask two different questions.

Power output and stored energy describe different limits. Ask what can run at once and what runtime the proposed load schedule could support. A useful answer includes starting charge, reserve, and assumptions about use.

Ask for a circuit-level proposal.

Request a marked list of backed-up circuits, any automatic load controls, and the method of utility isolation. Have the installer explain the equipment and any limitations in writing.