Solar Battery Bank Sizing

Calculate battery bank capacity for off-grid or backup power systems.

Daily energy consumption (Wh/day)

Use the Off-Grid Load Calculator to find this value.

Days of autonomy

Chemistry

Battery bank voltage

Individual battery voltage (V)

Typically 6V or 12V for lead-acid; 3.2V or 12V for LiFePO4.

Individual battery capacity (Ah)

From the battery label or spec sheet.

— Wh capacity needed

Total Wh capacity required —

Ah capacity at bank voltage —

Batteries in series (for voltage) —

Parallel strings (for capacity) —

Total batteries —

Usable capacity (with DoD & efficiency) —

Wiring configuration —

Chemistry	Depth of Discharge	Round-Trip Efficiency	Notes
Lead-acid flooded	50%	80%	Lowest cost, vented, regular maintenance
Lead-acid AGM/Gel	55%	80%	Sealed, no maintenance, higher cost
LiFePO4	80%	95%	Best overall — longer cycle life, safer chemistry
Lithium NMC	70%	97%	High energy density, used in EVs and some storage

Weight estimates: Lead-acid ≈ 6 lbs/Ah · LiFePO4 ≈ 1.5 lbs/Ah