How Big a Battery Do You Actually Need?
The right battery size isn’t a round number on a brochure. It’s the answer to “what do you want to keep running, and for how long?”
Battery capacity is measured in kilowatt-hours (kWh) — energy — while what a battery can run at once is measured in kilowatts (kW) — power. You need enough of both. Here’s the practical method.
Step 1: List what you want to back up
Essentials only (furnace fan, fridge, lights, internet, well pump, a few outlets)? Or the whole home including AC and range? The list drives everything. Try our battery sizing tool to add it up.
Step 2: Estimate the energy
Add up the daily kWh of those loads and decide how many hours of backup you want. Essential-load coverage often points to 10–20 kWh; whole-home or multi-day to 30 kWh+. Most modern batteries are modular, so you can stack capacity.
Step 3: Check the power (kW) and surge
Some appliances — well pumps, AC compressors, some furnaces — spike hard at startup (surge). The battery’s continuous and peak kW rating must cover those spikes, or the lights flicker when the pump kicks on.
Step 4: Account for Minnesota cold
Cold can reduce usable capacity and outages here often happen in winter, so we size with a margin and locate batteries in conditioned space where possible (see indoor battery code).
Frequently asked.
Can I add more battery later?
Yes — Enphase, EG4 and HomeGrid systems are modular, so you can start with essential-load backup and stack more capacity later.
What's the difference between kW and kWh?
kWh is how much energy is stored (runtime); kW is how much power it can deliver at once (how many things can run together). You need both sized right.
Have a question we haven't covered?
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