Battery & Runtime Calculator
Find out how long a battery bank will run a given load — or how much battery you need to run your gear for a set number of hours.
A · How long will my battery last?
Runtime estimate
—
B · How much battery do I need?
Battery required
— Ah
Skilled Deep-cycle batteries only — never use car/starting batteries for storage.
How this calculator works
A battery's nameplate capacity is not what you can actually use. Three things reduce it:
- Depth of discharge (DoD): draining a lead-acid bank below ~50% shortens its life dramatically; LiFePO₄ can safely use ~85% (often 90–100% in some designs).
- Inverter & wiring losses: converting DC to AC loses roughly 10% — we assume 90% efficiency (0.9).
- Peukert effect & temperature: lead-acid delivers less capacity at high discharge rates and in cold weather; lithium is far less affected.
The formulas are:
- Usable energy:
Ah × volts × DoD × 0.9→ watt-hours (Wh). - Runtime:
usable Wh ÷ load (W)→ hours. - Required capacity:
load (W) × hours ÷ (volts × DoD × 0.9)→ Ah.
Caveats
- Motor loads (fridges, pumps) draw a 3–5× surge on start-up — allow headroom.
- Real-world runtime is usually shorter than the math suggests; treat results as a planning estimate.
- Lead-acid needs regular full recharges; chronic under-charging is the #1 cause of early failure.