Battery Bank Size Calculator
Enter your daily energy need and design choices (DoD, autonomy) to get the bank size in Ah and kWh, plus how many battery blocks to arrange.
Last updated: 2026-09-15
How the calculation works
- Daily energy × autonomy days gives the reserve energy; dividing by DoD sizes the physical bank so you never cross the discharge limit.
- Bank Ah follows from the system voltage; the tool shows typical 200 Ah block counts for series/parallel layout.
Formula
Bank Wh = daily Wh × autonomy ÷ DoD Bank Ah = Bank Wh ÷ system V
| Symbol | Meaning | Unit |
|---|---|---|
DoD | Usable depth of discharge | — |
Ah | Ampere-hour capacity | Ah |
Worked example
Interpreting the result
The DoD choice dominates: the same usable energy needs a 100 Ah lithium bank or a 160 Ah AGM bank (0.8 vs 0.5 DoD) — and lithium lasts 3–5× more cycles, which is why the premium pays off in cycle-lifetime cost. Autonomy days set how you ride out clouds; more days = bigger bank but a smaller generator dependence.
Assumptions
- Constant daily load across the autonomy period.
- Batteries at moderate temperature; cold derates capacity.
Limitations
- High charge/discharge rates (Peukert) reduce effective lead-acid capacity below the rated figure.
- Aging: replace the bank at ~80% of rated capacity.
Frequently asked questions
How many batteries for a 12V off-grid cabin?
Depends on load: 1 kWh/day at 50% DoD and 2 days autonomy = 4 kWh = 333 Ah @ 12 V — four 100 Ah batteries in parallel, or better, one 12 V 300 Ah+ lithium.
Should I go 12V, 24V or 48V?
Above ~1,500 W continuous or ~1,000 Ah, go 24 V; above 3 kW, 48 V. Higher voltage cuts current, cable size and losses for the same power.