Battery Runtime Calculator
Estimate how long a battery will last from capacity and load—instant battery life / runtime for DC packs (Ah, V, A or W). Not a UPS inverter model.
Calculator
Quick: Ah + load amps → hours. Advanced: mAh/Wh, watts load, DoD, efficiency, or reverse Ah sizing.
About this calculator
This battery runtime calculator (also called a battery life calculator) estimates hours from DC capacity and load. It is not an APC/Eaton UPS selector and not a multi-day solar autonomy tool. For UPS inverter packs use UPS runtime; for Ah procurement use UPS battery sizing. Browse the power calculator hub.
Calculation Results
≈ 20.00 hours (20 h)
100 Ah · 5 A · DoD 1.00 · η 1.00
Formula: hours = (Ah × DoD × η) ÷ I
Assumptions: constant average load; Peukert / high C-rate capacity loss is not modeled (real hours can be shorter than this screen). Temperature and pulsed loads also matter—treat as planning only.
Battery runtime quick reference
Ideal hours at DoD 1.0 and η 1.0 (no Peukert). Open a row to load the calculator.
| Pack | Load | Ideal runtime |
|---|---|---|
| 1 A | 7 h | |
| 5 A | 20 h | |
| 200 W | 6 h | |
| 200 W · DoD 0.8 | ≈ 4.6 h | |
| 200 W | 12 h | |
| 500 W · DoD 0.8 | ≈ 7.3 h | |
| 100 mA | 20 h |
Battery runtime formula & explanation
hours = (Ah × DoD × η) ÷ I
With a watt load: hours = (Ah × V × DoD × η) ÷ W (same as converting W to amps with I = W ÷ V).
Peukert note: This calculator uses a linear energy balance (like DigiKey/Omni capacity ÷ current screens with a safety/DoD factor). It does not apply Peukert’s law—high discharge rates reduce available Ah, so field runtime can be shorter.
- Ah — amp-hour capacity (mAh ÷ 1000; Wh ÷ V).
- DoD — usable fraction of nameplate capacity (chemistry presets above).
- η — DC path / converter efficiency (≤ 1).
- I / W — average load current or power.
Example: 100 Ah, 12 V, 60 W, DoD 1.0, η 1.0 → I = 5 A → 20 hours.
Wh ↔ Ah converter: ampere hour to watt hour calculator. Ah ÷ hours → A: Ah to amps calculator. Solar multi-day bank sizing: solar battery bank / autonomy. UPS minutes: UPS runtime calculator.
When to use which battery tool
| Goal | Tool |
|---|---|
| DC pack hours from Ah / V / load | This page — battery runtime |
| UPS backup minutes (inverter + kVA) | UPS runtime calculator |
| Required Ah for UPS target minutes | UPS battery sizing |
| Series/parallel string layout | UPS battery bank |
| Solar days of autonomy (kWh) | Solar battery bank calculator |
Frequently Asked Questions
How do I calculate battery runtime?
Hours ≈ (Ah × DoD × η) ÷ I. With watts: hours ≈ (Ah × V × DoD × η) ÷ W. Example: 100 Ah at 12 V into 60 W ≈ 20 hours at ideal DoD/η.
How long will a 100Ah battery last with a 200W load?
At 12 V ideal: hours ≈ (100 × 12) ÷ 200 = 6 hours. With LiFePO4 planning DoD 0.8 and η 0.95 ≈ 4.6 hours. Use the 100 Ah · 12 V · 200 W or LiFePO4 quick example above. At 24 V the same 100 Ah lasts about twice as long at the same watts.
Is this a lithium / LiFePO4 battery runtime calculator?
Yes for DC packs—enter Ah, V, and load. Use DoD ≈ 0.8–0.9 for many LiFePO4 packs (shallower than lead-acid 0.5). It is still an energy-balance screen, not a BMS or Peukert model.
Is this a battery life calculator?
Yes. Battery life and battery runtime here mean how long a DC pack can power a constant load. Enter Ah/mAh/Wh and A/mA/W above.
How is this different from a UPS runtime calculator?
This page is a DC energy-balance screen. The UPS runtime calculator models inverter efficiency, UPS kVA headroom, and OEM-oriented backup minutes.
How do I convert Wh to Ah?
Ah = Wh ÷ V. Example: 120 Wh at 12 V = 10 Ah. Use the dedicated ampere hour to watt hour calculator, or select Wh as capacity unit here and enter voltage.
How do I calculate battery runtime from capacity and average current?
Hours ≈ (Ah × DoD × η) ÷ I—the same capacity ÷ average current idea used on DigiKey-style battery life screens, plus optional DoD/η. Example: 100 Ah ÷ 5 A ≈ 20 hours at DoD 1.0. Peukert is not modeled.
Does depth of discharge change runtime?
Yes. Usable Ah ≈ nameplate × DoD. At DoD 0.5, planned hours are about half the DoD 1.0 ideal case before other losses. Use the chemistry presets (lead-acid / LiFePO4) to seed DoD, then fine-tune.