Nor’easters and ice storms knock out power across Massachusetts every winter, sometimes for days. A home battery keeps the essentials running. The question we get most: how long?
The honest math
A 10 kWh battery (like the Enphase IQ Battery 10P) stores about 10,000 watt-hours. Divide that by your continuous load to get hours of runtime. Running just the essentials, refrigerator (~150 W), LED lights (~100 W), Wi-Fi and phones (~50 W), draws about 300 W, which is roughly 30+ hours on one battery. Add a medical device or the furnace fan and it drops; add a second battery and it doubles.
You can model your own home on the batteries page, pick your appliances and battery count and it estimates the runtime live.
The cold-weather caveats
- Heat is the big load. A mini-split heat pump pulls ~1,200 W per zone. Backing up whole-home heating during a multi-day outage usually needs two or more batteries, or a strategy of heating one room.
- Batteries like to stay warm. We install Enphase units in conditioned or semi-conditioned space (basement, not an unheated detached garage) so cold doesn’t reduce capacity.
- Storm Guard pre-charges. Enphase’s Storm Guard watches the weather forecast and tops the battery to 100% before a predicted storm, so you start the outage full.
How to size it
We start from what you actually want to keep on, not from a sales tier. List your must-haves (fridge, lights, internet, medical, maybe one heating zone), add the watts, and pick the battery count that covers a realistic 2–3 day MA outage. Most homes land at one or two batteries. We size it with you before you sign anything, no guessing, no over-selling.