Usable capacity is the energy available from the battery, measured in kilowatt-hours (kWh). Compare the usable figure, rather than just the advertised total, with your evening and overnight use. Energy reserved for an outage reduces what is available for everyday bill savings.
Power output, measured in kilowatts (kW), is the amount the battery can supply at one time. An oven and heating running together can need more power than lights and a fridge. A larger store of energy does not automatically increase that output limit.
For backup, ask for the specific circuits that will remain powered, any appliance restrictions and how your household’s electrical supply affects the design. Confirm whether solar can recharge the battery during an outage. Backup duration varies with charge level and the appliances you run.