Battery Run Time Calculator

Estimate 12V battery run time from Ah and watts—100 Ah at 12 V and 200 W lasts about 6 hours. Not a UPS inverter model.

Calculator

Quick: Ah + load amps → hours. Advanced: mAh/Wh, watts load, DoD, efficiency, or reverse Ah sizing.

Calculation mode

Battery capacity

Nameplate capacity. Wh mode divides by voltage to get Ah.

Battery voltage (V)

Required for Wh capacity or watt loads. DigiKey-style current path works without V when load is in amps.

Load

Average draw. Watts path uses I = W ÷ V.

Battery chemistry (sets DoD / η defaults) Matches OEM runtime screens that ask chemistry—then tune DoD like Omni’s discharge safety margin.

Usable depth of discharge (DoD, 0–1) 1.0 = full nameplate (ideal). Lead-acid often 0.5; many LiFePO4 packs ~0.8–0.9.

Path efficiency η (0.5–1) Include converter/wiring losses if known. Default 1.0 for ideal DC screen.

About this calculator

This battery run time calculator (also called a battery runtime calculator or battery life calculator) estimates hours for a DC pack, including 12V Ah and watt loads. 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.

Continue Your Calculation

Need amp-hours for a target run time instead of hours? Switch to required Ah on this calculator.

Required Ah →

UPS inverter minutes: UPS runtime calculator.

12V battery run time examples

How long does a 12V battery last?

For a 12 V pack, hours ≈ (Ah × 12 × DoD × η) ÷ watts. At DoD 1.0 and η 1.0, a 7 Ah battery at 1 A lasts 7 hours, and a 100 Ah battery at 200 W lasts 6 hours. A 200 Ah battery at 12 V and 200 W lasts 12 hours on that ideal path; with LiFePO4 DoD 0.8 and η 0.95 the same load lasts 9.12 hours.

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	12 h
	200 W · DoD 0.8	9.12 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 run time 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

What moves runtime beyond the entered DoD and efficiency

The calculator applies the usable depth of discharge and the path efficiency you enter. Four further factors explain why a measured runtime usually lands below the arithmetic result — they are the reason a nameplate amp-hour figure is a starting point, not an answer.

Factor	Effect on usable runtime	Planning step
Depth of discharge vs cycle life	Cycling deeper buys runtime per discharge but consumes the service life faster: a 50% DoD duty typically yields a multiple of the cycles available at 80% DoD on the same cell.	Pick the DoD from the replacement interval you can actually service, not from the longest single discharge.
Temperature	Nameplate capacity is quoted near 25 °C. Cold cells deliver less of it on the same load, and sustained heat above the reference accelerates capacity fade.	Use the manufacturer's temperature-correction table for the coldest expected room, and treat a hot battery room as a life-reduction issue.
Discharge rate (hour-rate rating)	Rated amp-hours are stated at a reference hour rate (C20 is common for lead-acid blocks). Drawing the same bank faster than its reference rate delivers fewer amp-hours.	Read the vendor hour-rate table at your actual discharge time instead of scaling the C20 rating linearly.
Ageing / end of life	End of life is normally declared at a fraction of rated capacity (often 80%), so an aged bank reaches the calculated hours before the fresh-bank result.	Size on the end-of-life capacity you are willing to accept, then check interim years with a discharge test.

The full derating treatment — vendor-style tables, depth-of-discharge and temperature modules — is in the UPS battery calculator. For what capacity fade does to runtime over the service life, see the UPS battery aging guide.

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.

How many hours is a 200Ah battery?

At 12 V and 200 W, ideal hours ≈ (200 × 12) ÷ 200 = 12 hours. With LiFePO4 DoD 0.8 and η 0.95 the same load lasts (200 × 12 × 0.8 × 0.95) ÷ 200 = 9.12 hours. At 100 W the ideal runtime is about 24 hours. Open the 12 V · 200 Ah row above to load this case. This is a DC energy balance, not a UPS inverter model.

How do I calculate 12V battery run time?

Hours ≈ (Ah × 12 × DoD × η) ÷ watts. Example: 100 Ah at 200 W, DoD 1.0 and η 1.0 = 6 hours. A 7 Ah battery at 1 A lasts 7 hours. Enter 12 V above, or use the 12 V preset.

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.

Is this a battery run time calculator or battery backup calculator?

Yes for DC packs. Battery run time calculator and DC-oriented battery backup calculator searches map here (Ah × V ÷ W with DoD/η). If you mean UPS wall/inverter backup minutes, switch to the UPS runtime calculator.

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.