Battery Bank Size Calculator 2026: Off-Grid kWh & Ah
Size an off-grid or backup battery bank in 2026: enter daily watt-hours, days of autonomy, battery type and voltage to get kWh, amp-hours and estimated cost.
Estimate scope & data quality
This tool provides an input-driven estimate. Use the required inputs shown above and review the result limitations below.
- Data quality
- NOT_AVAILABLE
- Result limitation
- Calculator output is not a source-complete customer result.
A tariff credit is distinct from annual savings. If a result is NOT_COMPUTABLE or CONFLICT, it must not be replaced with an estimate or treated as canonical.
How to use this calculator
- Add up your daily energy use in watt-hours (Wh): each appliance's watts × hours used per day.
- Choose days of autonomy: how many days the bank must run with little or no solar input (1 day for backup, 2–3 days for most off-grid cabins, more in cloudy climates).
- Pick your battery chemistry. LiFePO4 lithium is modeled at 80% usable depth of discharge; lead-acid (AGM or flooded) at 50%.
- Pick your system voltage (12 V, 24 V or 48 V) to see the bank size in amp-hours.
- Enter your battery price per kWh and any confirmed rebate to see the estimated cost. No federal tax credit applies to batteries installed in 2026.
Understanding your results
Battery bank size (kWh) = (daily Wh × days of autonomy) ÷ (depth of discharge × 0.90). The 0.90 factor covers inverter and wiring losses when you run AC loads. Example: 3,000 Wh/day × 2 days ÷ (0.80 × 0.90) = 8,333 Wh, or about 8.3 kWh of nameplate LiFePO4 capacity.
Amp-hours (Ah) = bank Wh ÷ system voltage. The same 8.3 kWh bank is about 694 Ah at 12 V, 347 Ah at 24 V or 174 Ah at 48 V. Higher voltage means lower current, thinner cables and less loss, which is why most whole-home and larger off-grid systems use 48 V.
Depth of discharge (DoD) is how much of the battery you plan to use each cycle. LiFePO4 batteries routinely handle 80–90% DoD. Lead-acid batteries last far longer when kept above 50% charge, so you need roughly 60% more nameplate capacity for the same usable energy.
Cost = bank kWh × your price per kWh, minus any rebate you enter. DIY LiFePO4 modules often sell for a few hundred dollars per kWh of capacity (hardware only); professionally installed whole-home batteries run about $12,000–$16,000 for a 13.5 kWh unit, or roughly $900–$1,200 per kWh. Get current quotes; prices vary widely.
Federal tax credit: none for 2026 installs. Batteries of 3 kWh or more used to qualify for the 30% Residential Clean Energy Credit (§25D) until Dec 31, 2025. The One Big Beautiful Bill Act (Public Law 119-21) ended it for batteries installed after that date (IRS FAQ). This is not tax advice; confirm with a tax professional.
Frequently asked questions
Direct answers for US homeowners.
Related guides
In-depth articles on sizing, costs, and energy decisions.