How to Calculate Battery Capacity Step by Step

In depth

Step 2: divide by system efficiency (about 0.9 for the inverter) to get the energy the battery must deliver.

Step 3: divide by allowed depth of discharge - 0.9 for LiFePO4, 0.5 for gel. The result is the nameplate capacity you need in kWh.

Step 4: convert to amp-hours by dividing by system voltage: Ah = (kWh x 1000) / V. Example: 15kWh at 51.2V is about 293Ah.

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Common mistakes to avoid

• Comparing amp-hours only and ignoring voltage, ending up with four times less energy than needed
• Discharging lead acid below 50%, which cuts life to less than half
• Picking a bank that does not match the inverter voltage, so charging fails or runs inefficiently
• Thin cable or a long run between bank and inverter, causing voltage drop and lost power
• Mixing new and old packs, or different capacities, on the same bus

Next step

Send your load list and required hours over WhatsApp, or use the on-site system calculator to size the battery bank and array.

Technical advice is free, and the recommendation is based on your real consumption, inverter voltage and installation location rather than on the largest battery in stock.

Frequently asked questions