Free sizing tool
Battery Bank Size Calculator (12V/24V/48V)
Tell this tool how much power you use in a day and how many cloudy days you want to ride out. It works out the battery bank you need in watt-hours and amp-hours, how many batteries that takes, and exactly how to wire them in series and parallel for 12V, 24V, or 48V. No formulas on your end.
How to use this
- Add up roughly how many watt-hours you use in a day. A small van might use 500 to 1,000 Wh, a cabin 2,000 to 5,000 Wh. The appliance chart linked below helps.
- Pick your days of autonomy, meaning how many days the bank should run things with no charging at all. One is fine if you have reliable sun or a generator. Two or three suits cloudy regions.
- Choose your system voltage and your battery chemistry. LiFePO4 lets you use about 80% of its capacity, lead-acid AGM only about 50%.
- Set a reserve buffer for headroom, pick a single battery size, then hit Calculate.
Your numbers
Not sure? A fridge, lights, and charging a few devices is around 1,000 to 2,000 Wh per day.
Days the bank runs with no charging. Try 1 with good sun, 2 to 3 if cloudy.
We treat each battery as a 12V nominal module, which is the standard for 100Ah class batteries.
Keep going
- LiFePO4 voltage chart, to read state of charge from the battery voltage.
- Appliance power consumption chart, to nail down your daily watt-hours.
- How to size an off-grid solar system, the full walkthrough behind these numbers.
- 12V vs 24V vs 48V off-grid, to pick the right system voltage before you buy.