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Battery Runtime & Life Cycle Calculator (LiFePO4, AGM, UPS)

Calculate battery discharge runtime, usable watt-hours, and lifecycle longevity under inverter loads.

Last reviewed by the myCalculator Editorial Team

Input Parameters

Ah

e.g. 100Ah 12V lithium deep-cycle battery

Volts

12V, 24V, or 48V battery bank

W

e.g. 60W portable 12V fridge, 150W TV/lighting, 1000W microwave

%

DC to 240V AC pure sine wave inverters operate at 85% to 92% efficiency

Calculation Results

Estimated Usable Battery Runtime
4h 52m (4.9 hours)
Total Usable Energy
1,080 Wh (90% Safe DoD of 1,200 Wh)
Continuous Discharge Current
18.5 Amps @ 12V (0.19C rate)
Battery Chemistry & Cycle Life
Lithium Iron Phosphate (LiFePO4) (~4,000 cycles)
Effective DC Load (with Inverter)
222.2 Watts (90% inverter efficiency)
Summary: A 100Ah 12V (1200 Wh) Lithium Iron Phosphate (LiFePO4) battery running a 200W load (222.2W with 90% inverter) delivers 4 hours and 52 minutes of continuous runtime down to a safe 90% depth of discharge.

Visual Growth Breakdown

Step-by-Step Calculation Solution
1.Nominal Capacity = 100 Ah × 12 V = 1200 Wh
2.Safe Usable Energy = 1200 Wh × 90% = 1080 Wh
3.Total Load Drawn = 200 W ÷ (90% ÷ 100) = 222.2 W (18.52 A)
4.Runtime = Usable Energy (1080 Wh) ÷ Total Load (222.2 W) = 4.86 hours (4h 52m)

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Formula & How Battery Runtime & Life Cycle Calculator (LiFePO4, AGM, UPS) Works

Mathematical Formula
Usable Wh = (Ah × V) × DoD% | Total Load = Watts ÷ Inverter Eff | Runtime = Usable Wh ÷ Total Load

Runtime is the usable energy in the battery divided by the power the load draws, including inverter losses. A 100 Ah, 12 V battery stores 100 × 12 = 1,200 Wh. If you only use 80% of it, as is typical for lithium iron phosphate, the usable energy is 960 Wh. A 200 W load through a 90% efficient inverter draws 200 ÷ 0.9 = 222 W from the battery, so the runtime is 960 ÷ 222 = about 4.3 hours. Lead-acid and AGM batteries should usually be discharged less deeply, which shortens runtime. Real-world runtime is also lower in cold weather and at high discharge currents, so treat the result as a best case and leave a margin.

How to Calculate Battery Runtime & Life Cycle Calculator (LiFePO4, AGM, UPS) (Step-by-Step)
  1. Enter Battery Capacity Rating (Ah) (Ah): Input your target parameter value.
  2. Enter Nominal Battery Voltage (V) (Volts): Input your target parameter value.
  3. Enter Continuous Load (Watts) (W): Input your target parameter value.
  4. Enter Battery Chemistry Type: Input your target parameter value.
  5. Enter Inverter Efficiency (%) (%): Input your target parameter value.
  6. Apply Formula: Calculate using Usable Wh = (Ah × V) × DoD% | Total Load = Watts ÷ Inverter Eff | Runtime = Usable Wh ÷ Total Load.
  7. Review Results: View exact computed answers, metrics, and worked mathematical proofs.
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APA 7th Edition

MyCalculator.com.au. (2026). Battery Runtime & Life Cycle Calculator (LiFePO4, AGM, UPS). Retrieved October 24, 2026, from https://www.mycalculator.com.au/calculators/engineering/battery-life-runtime

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MyCalculator.com.au. (2026) 'Battery Runtime & Life Cycle Calculator (LiFePO4, AGM, UPS)'. Available at: https://www.mycalculator.com.au/calculators/engineering/battery-life-runtime (Accessed: 24 October 2026).

Frequently Asked Questions (FAQs)

How long will a 100Ah 12V battery run a 200W load?

A 100Ah 12V LiFePO4 battery (90% DoD = 1,080 Wh usable) running a 200W AC load through a 90% efficient inverter (222W draw) will run for approximately 4.8 to 5.0 hours. An AGM battery (50% DoD = 600 Wh usable) will last only ~2.7 hours.

Why does lead-acid AGM last shorter than Lithium LiFePO4?

Lead-acid batteries suffer from Peukert's Law (capacity drops drastically under heavy loads) and cannot be discharged past 50% without shortening their lifespan. Lithium batteries maintain stable voltage output down to 90% discharge.

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Independent & Verified

Calculations and mathematical logic on this page are grounded in published statutory rules, regulatory standards, and official government data published by the following bodies:

Standards AustraliaOfficial Standard
Peak Non-Government Standards Organization

Australian Standards including AS/NZS 3000 (Wiring Rules), AS 3600 (Concrete Structures), and AS 4100 (Steel Structures).

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Engineers AustraliaIndustry Partner
National Engineering Professional Body

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