What is depth of discharge (DoD)?

DoD is the percentage of a battery's capacity you can safely use before recharging. Lead-acid batteries should not go below 50% DoD or their lifespan drops sharply. Lithium (LiFePO4) batteries tolerate 80–90% DoD without damage.

Why does system efficiency matter?

Energy is lost in the inverter, wiring, and charge controller. A typical off-grid system runs at 80–90% round-trip efficiency. Using 85% is a common and conservative estimate. Ignoring losses leads to an undersized bank.

What voltage should I choose for my system?

12V suits small systems under ~1,000W. 24V is common for mid-size cabins. 48V minimizes wire losses for larger systems (3 kW+). Higher voltage = lower current = thinner wires for the same power.

How do I convert Ah to number of batteries?

Divide the required Ah by the Ah rating of one battery. Example: 400 Ah required ÷ 100 Ah per battery = 4 batteries wired in parallel (at the same voltage).

Is this calculator accurate for lithium batteries?

Yes. Set DoD to 80% (or the manufacturer's recommended value) and the calculator correctly sizes the bank. Lithium banks come out smaller than lead-acid banks for the same usable capacity.

Solar Battery Bank Size Calculator

Name: Solar Battery Bank Size Calculator
Availability: InStock
Author: Nham Vu

Calculate the required battery bank capacity in Ah and Wh for an off-grid solar system.

System Parameters

Daily Energy Consumption (Wh/day)

Total watt-hours your loads consume per day.

Autonomy Days (days without sun)

How many consecutive cloudy days the bank must cover.

Battery Bank Voltage (V)

Depth of Discharge — DoD: 50%

20% (very conservative) 95% (max lithium)

50% for lead-acid • 80% for lithium (LiFePO4).

System Efficiency: 85%

60% (high losses) 98% (near-ideal)

Accounts for inverter, wiring, and charge controller losses. 85% is typical.

Enter your system parameters and click Calculate to see the required battery bank size.

Battery Type Quick Guide

Lead-Acid (FLA / AGM) DoD 50% • ~500 cycles

Lithium (LiFePO4) DoD 80% • 2,000–5,000 cycles

Gel / VRLA DoD 50–60% • ~600 cycles

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Summary

Calculate the required battery bank capacity in Ah and Wh for an off-grid solar system.

How it works

Enter your total daily energy consumption in watt-hours (Wh/day).
Set the number of autonomy days — how many sunless days the bank must cover.
Choose your battery bank voltage (12V, 24V, or 48V).
Set the depth of discharge (DoD): 50% for lead-acid, 80% for lithium.
Set the system efficiency (typically 85%) to account for inverter and wiring losses.
The calculator outputs the required capacity in both Ah and Wh.

Use cases

Size a battery bank for an off-grid cabin or tiny home.
Plan backup power storage for a grid-tie solar system.
Compare lead-acid vs. lithium battery bank requirements.
Verify an existing battery bank covers your daily loads plus autonomy buffer.
Design a van or RV solar system with the right Ah rating.
Calculate how many 100Ah batteries you need by dividing the result.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu