CalcPanel

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.

Nameplate capacity. Wh mode divides by voltage to get Ah.
Required for Wh capacity or watt loads. DigiKey-style current path works without V when load is in amps.
Average draw. Watts path uses I = W ÷ V.
Matches OEM runtime screens that ask chemistry—then tune DoD like Omni’s discharge safety margin.
1.0 = full nameplate (ideal). Lead-acid often 0.5; many LiFePO4 packs ~0.8–0.9.
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 A7 h
5 A20 h
200 W6 h
200 W12 h
200 W · DoD 0.89.12 h
200 W · DoD 0.8≈ 4.6 h
200 W12 h
500 W · DoD 0.8≈ 7.3 h
100 mA20 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 / loadThis page — battery runtime
UPS backup minutes (inverter + kVA)UPS runtime calculator
Required Ah for UPS target minutesUPS battery sizing
Series/parallel string layoutUPS 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 lifeCycling 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.
TemperatureNameplate 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 lifeEnd 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.

24V and 48V battery run time examples

How long does a 24V battery last?

Same formula with the pack voltage: hours ≈ (Ah × 24 × DoD × η) ÷ watts. A 100 Ah 24 V pack into a 400 W load lasts 6 hours at ideal DoD 1.0 and η 1.0; with LiFePO4 DoD 0.8 and η 0.95 it lasts 4.56 hours. Halve the load to 200 W and the ideal case doubles to 12 hours.

How long does a 48V battery last?

Hours ≈ (Ah × 48 × DoD × η) ÷ watts. A 100 Ah 48 V bank into a 2400 W load — typical of a small inverter or solar-storage draw — lasts 2 hours ideal; into 1200 W it lasts 4 hours. 48 V banks are common in off-grid inverters and telecom DC plants, where the same Ah carries twice the energy of a 24 V pack.

Series and parallel battery banks: what changes runtime

Wiring changes voltage and capacity, and the formula tracks both. Series adds voltage: two 12 V 100 Ah blocks in series make a 24 V 100 Ah bank, so a 240 W load runs (100 × 24) ÷ 240 = 10 hours ideal. Parallel adds capacity: the same two blocks in parallel make a 12 V 200 Ah bank, and a 120 W load runs (200 × 12) ÷ 120 = 20 hours ideal. Total stored energy (Ah × V) is the same either way — the load voltage decides which wiring delivers it, and runtime follows from energy ÷ load.

All bank examples are ideal DC energy balance at DoD 1.0 and η 1.0 (no Peukert, no wiring losses). Enter your bank's actual voltage and Ah above, or open a row in the 12 V table to load the 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.

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.

What is the difference between battery run time and battery life?

Battery run time is how long one charge powers your load — the single-discharge hours this page computes. Battery life can also mean cycle life: how many charge/discharge cycles a pack delivers before capacity fades. This page models the first, not cycle aging; for runtime degradation across the service life, see the UPS battery aging guide.

How do I calculate run time for a 24V or 48V battery bank?

Same formula with the bank voltage: hours ≈ (Ah × V × DoD × η) ÷ W. A 24 V 100 Ah pack into 400 W lasts (100 × 24) ÷ 400 = 6 hours ideal; a 48 V 100 Ah bank into 2400 W lasts 2 hours. For series/parallel banks, first convert to bank voltage (series counts add per-block voltage) and bank Ah (parallel strings add Ah), then apply the formula. See the 24V/48V examples section above.