Skip to content

Federal rebates for gas-to-electric heating conversions have ended — but electric-to-heat-pump upgrades still qualify. What changed

Battery Runtime Estimator

A quick, transparent estimate of how long a home battery could keep the lights on during an outage — pick what you'd back up and see the math.

Your Battery & Loads

Default of 13.5 kWh is roughly one Tesla Powerwall 3. Enter your actual usable capacity if you know it.

What would you back up?

Check the loads to power during an outage, and adjust their average wattage if you know it runs differently.

W
W
W
W
W
W
W
W
W

Estimated Runtime

roughly 31h 58m

Total draw (5 loads)
380 W
Usable capacity (rated)
13.5 kWh
Usable capacity (after ~10% losses)
12.15 kWh

We derate rated capacity by ~10% to account for round-trip and inverter losses before estimating runtime.

Rough estimate only

This is a simplified, educational estimate — not a guarantee. Actual runtime depends on real appliance draw (which often spikes on startup), battery age and condition, temperature, and how your system is configured. Consult a licensed installer for a real load calculation before relying on backup power.

Your entries are saved in this browser so they're here next time. Nothing is sent anywhere.

How This Estimate Works

  1. Total draw = sum of the wattage of every load you check.
  2. Usable capacity = the battery's rated usable kWh × ~0.9, to account for round-trip and inverter losses.
  3. Runtime = usable capacity (kWh) ÷ total draw (kW).

This tool is intentionally simple. It doesn't model appliance duty cycles (a fridge or well pump doesn't run continuously), battery degradation, temperature effects, or exact solar recharge — all of which a real installer's load calculation should address. Treat the result as a back-of-envelope starting point, not a substitute for a professional assessment.

Guides that explain these numbers

Other calculators

Get the next guide

Occasional emails when we publish a new cost breakdown or update an existing guide with current pricing. No sales calls, no installer lists, unsubscribe anytime.

Follow via RSS

You can also subscribe by RSS.