Battery Runtime Calculator
How long will a battery last? It depends on capacity (Ah), voltage, how deeply you are willing to discharge it, inverter efficiency, and the load. This calculator combines all five into one honest runtime figure — the number most product listings skip.
Formula: Runtime (hours) = Ah × V × DoD × efficiency ÷ load watts
Worked example: a 100 Ah, 12 V battery running a 200 W load at 80% depth of discharge and 90% inverter efficiency: 100 × 12 × 0.80 × 0.90 ÷ 200 = 4.32 hours (about 4 hours 19 minutes). Using 100% depth of discharge would claim 6 hours — and kill a lead-acid battery quickly. Lithium batteries tolerate 80–90% DoD; lead-acid should stay near 50% for a long life.
Sizing a solar system to charge that battery? Use the solar PV sizing calculator.
Frequently asked questions
What depth of discharge should I use?
Lead-acid: 50% for long life. Lithium (LiFePO4): 80–90% is normal. Deeper discharges give longer runtimes on paper and shorter battery life in practice.
Why does the runtime fall short in cold weather?
Battery capacity drops with temperature, and inverter efficiency falls at very light loads. Treat the result as a good-conditions estimate and keep margin for winter.
Does a bigger inverter help?
No — an oversized inverter running a tiny load is less efficient, not more. Size the inverter close to the actual load for the best efficiency.