Battery Run Time Calculator

Advanced Battery Run Time Calculator

Battery capacity

Capacity unit

Voltage per battery

Batteries in series

Parallel strings

Load type

Load value

Efficiency percent

Depth of discharge percent

Battery age factor percent

Temperature factor percent

Reserve percent

Peukert exponent

Reference hour rating

Formula Used

The calculator first converts stored capacity into watt hours.

For Ah: watt hours = amp hours × system voltage.

For mAh: amp hours = mAh ÷ 1000.

For Wh: total watt hours = Wh per battery × series count × parallel count.

Usable energy: nominal Wh × discharge limit × age factor × temperature factor × reserve factor.

Battery draw: load watts ÷ efficiency.

Ideal runtime: usable Wh ÷ battery draw watts.

Peukert estimate: reference hours × (usable Ah ÷ battery current ÷ reference hours)^{Peukert exponent}.

The final runtime uses the lower value from ideal runtime and Peukert runtime.

How to Use This Calculator

Enter the battery capacity and choose Ah, mAh, or Wh.
Enter the voltage for one battery.
Add batteries in series and parallel strings.
Enter the load in watts or amps.
Add efficiency, discharge limit, age, temperature, and reserve values.
Use Peukert exponent near 1.00 for lithium batteries.
Use higher Peukert values for lead acid batteries.
Press the calculate button to view the result above the form.
Use CSV or PDF buttons to save the same calculation.

Example Data Table

Battery Setup	Load	Efficiency	Discharge Limit	Estimated Use Case
12 V, 100 Ah, 1S1P	100 W	90%	80%	Router, lights, small fan
12 V, 200 Ah, 1S2P	300 W	88%	70%	Workshop backup
12 V, 100 Ah, 2S1P	500 W	92%	85%	24 V inverter bank
48 V, 100 Ah, 1S1P	800 W	94%	90%	Solar storage system

Battery Run Time Guide

A battery run time calculator estimates how long stored energy can support a load. It helps users compare battery sizes, load demand, and realistic loss factors. Simple division can mislead results. Real systems lose energy through wiring, inverters, age, temperature, and discharge limits.

Why Runtime Changes

Battery capacity is usually listed in amp hours or watt hours. Amp hours need voltage before energy is known. Watt hours already describe stored energy. A 100 Ah battery at 12 volts has about 1200 watt hours before adjustments. Only part of that energy should be used. Deep discharge can shorten life. Lead acid batteries usually need higher reserves. Lithium batteries often allow deeper discharge.

Important Input Factors

Load size is the largest driver. A 300 watt load drains energy faster than a 50 watt load. Efficiency also matters. An inverter rated at 90 percent makes the battery supply more power than the appliance uses. Age lowers capacity over time. Cold temperatures can reduce available energy. High discharge current can reduce effective capacity, especially in lead acid batteries. This is why the Peukert exponent is included.

Planning Better Backup Systems

Use the calculator before buying batteries or connecting equipment. Enter capacity, voltage, battery count, and load demand. Then adjust depth of discharge, efficiency, age, temperature, and reserve. The result gives runtime in hours and minutes. It also shows usable watt hours and estimated current. These values help compare several designs.

Practical Safety Notes

Keep reserve time for shutdowns, alarms, pumps, routers, or medical devices. Never size a battery to run at its exact limit. Use proper fuses, cables, terminals, and ventilation. Check the battery maker data sheet for maximum current. The calculator gives an estimate, not a safety certification. Field measurements can differ because batteries and loads change during use.

Best Use Cases

This tool is useful for solar backups, UPS planning, camping power, telecom cabinets, security systems, and small workshops. It can also compare series and parallel battery banks. Review results often when loads change. A small extra margin can improve reliability and battery life.

For critical sites, test runtime monthly. Record voltage trends, current, ambient temperature, and cut off settings. Better records improve future sizing decisions and maintenance.

FAQs

What is battery run time?

Battery run time is the estimated time a battery can power a load before reaching the selected discharge limit.

Why is efficiency included?

Efficiency accounts for inverter, wiring, and conversion losses. A lower efficiency value means the battery must supply more energy.

What is depth of discharge?

Depth of discharge is the usable portion of battery capacity. A lower value protects battery life but reduces runtime.

What Peukert value should I use?

Use about 1.00 to 1.05 for lithium batteries. Use higher values, such as 1.10 to 1.30, for lead acid batteries.

Can I enter load in amps?

Yes. Choose amps as the load type. The calculator converts current to watts using the calculated system voltage.

Does series wiring increase runtime?

Series wiring increases voltage. Energy also increases when more batteries are added. Runtime depends on total watt hours and load.

Does parallel wiring increase runtime?

Parallel wiring increases amp hour capacity. This normally increases stored energy and can improve runtime for the same load.

Is this calculator exact?

No. It gives a planning estimate. Real runtime depends on battery condition, temperature, cable loss, load changes, and manufacturer limits.