Earth Bondhon
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Rojony Khatun Author
Rojony Khatun
CalculatorToolsProjectExpert
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Małgorzata Koperska, MD Steven Wooding
Last updated: September 30, 2025

Battery Life Calculator | Runtime & Capacity Estimator

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Battery Life Calculator

Calculate battery life in hours. Enter capacity (Ah/Wh), load power, voltage, depth of discharge, and efficiency to find runtime.

battery discharge calculator

To estimate battery life, one needs to first convert battery capacity to usable energy. Multiplication of ampere-hours (Ah) by voltage (V) and depth of discharge (DoD), and efficiency is used. Divide by the load power in watts, then. The output provides approximated hours of run-time.

Formula & Table Summary:

Usable Energy (Wh): E = Ah × V × DoD × η

Battery Life (h): t = (Ah × V × DoD × η) ÷ P_load

Reverse (Required Ah): Ah_req = (P_load × t) ÷ (V × DoD × η)

battery usage time calculator

The calculation of the time period that a battery can support a load before needing a recharge is done using a battery life calculator. Run time in hours will be calculated by entering some battery capacity (Ah or Wh), system voltage, load power, depth of discharge (DoD), and efficiency. The tool can be applied to the backup systems, solar systems, electronics, UPS, and EVs. The formula is based on the available energy = Battery Capacity Voltage DoD Efficiency. This energy, divided by the load power, will achieve the expected run time. Divide system losses, inverter efficiency, and DoD restrictions to avoid excessive discharge and lengthen battery time.

battery runtime calculator

BatteryLoad (W)Voltage (V)DoDEfficiencyLife (h)
12V 100Ah100120.80.98.6
24V 150Ah300240.850.9210.4
48V 200Ah500480.90.9516.4
400V 62Ah20004000.90.912.5

Frequently Asked Questions - Battery Life Calculator:

How do I calculate battery life?

Multiply Ah × V × DoD × efficiency ÷ load (W).

What is depth of discharge?

DoD is the usable portion of capacity without damaging the battery.

Why include efficiency in battery life?

System and inverter losses reduce usable runtime.

How many hours will a 100Ah battery last?

At 12V, 100W load, DoD 80%, η 90%, runtime ≈ 8.6 h.

How to extend battery life?

Use lower DoD, efficient loads, and proper charging.

Can I calculate runtime in Wh instead of Ah?

Yes, Wh ÷ Load (W) = hours.

Does battery type affect DoD?

Yes, lead-acid ≈50%, lithium ≈80–90% recommended.

How do I size a battery for runtime?

Use Ah_req = (W×t) ÷ (V×DoD×η).

Does temperature affect runtime?

Yes, cold reduces available capacity.

What if load varies?

Use average load power or simulate in steps.

Rojony Khatun

Rojony Khatun

CalculatorToolsProject

Rojony Khatun is the creator of a free online tools website designed to simplify everyday and engineering-related calculations for students, professionals, and hobbyists. The platform offers a wide variety of basic and advanced calculators across key categories, including Electrical Calculators, Electronic Calculators, and Time & Date Calculators, helping users solve problems quickly and accurately.