Battery Backup Calculator for Home
Pick what must stay on during a cut and for how long - get the exact battery Ah and inverter VA you need.
What should stay on?
Fridge
TV
Wi-Fi + laptop
Your backup system
420 W
Connected load
250 Ah
Battery @12V (or 2.0 kWh)
600 VA
Inverter size
💡 You need 250 Ah - that is 2 lead-acid batteries or one lithium unit of 2.0 kWh. At this size, compare a solar + battery combo: the panels then recharge it free.
Assumes 85% inverter efficiency and 80% usable depth of discharge. Fridge compressors surge on start - the VA headroom covers it.
Frequently asked questions
Lead-acid or lithium?
Lead-acid is half the upfront price; lithium lasts 3x the cycles, charges faster and needs no maintenance. For daily cuts, lithium usually wins on cost per year.
Can solar charge this battery?
Yes - pair the same battery with panels and a hybrid inverter and outage backup becomes free solar storage. Size the solar side with our savings calculator.