Enter Battery And Load Details
Formula Used
System voltage = Battery voltage × Batteries in series
System amp hours = Battery Ah × Parallel strings
Nominal watt hours = System voltage × System amp hours
Usable watt hours = Nominal Wh × DOD × condition × temperature factor × reserve factor
DC input watts = Total load watts ÷ inverter efficiency
Runtime hours = Usable watt hours ÷ DC input watts
DC current = DC input watts ÷ system voltage
Required Ah = Required nominal Wh ÷ system voltage
How To Use This Calculator
Enter the rated voltage and amp hour value of one battery.
Add the number of batteries in series and parallel strings.
Enter your main load in watts. You can also enter amps.
Set inverter efficiency, discharge limit, condition, temperature, and reserve.
Press calculate. The runtime result appears above the form.
Use CSV or PDF buttons to save the calculated report.
Example Data Table
| Battery Setup | Voltage | Capacity | Load | Efficiency | Estimated Runtime |
|---|---|---|---|---|---|
| Single deep cycle battery | 12 V | 100 Ah | 300 W | 90% | About 2.28 hours |
| Two batteries in series | 24 V | 100 Ah | 500 W | 92% | About 3.35 hours |
| Four battery bank | 24 V | 200 Ah | 800 W | 90% | About 4.10 hours |
Battery Runtime Planning Guide
Why Runtime Estimates Matter
Battery runtime planning helps you avoid sudden power loss. It is useful for inverters, solar systems, camping power, emergency backup, UPS units, and mobile equipment. A battery may look large by its amp hour rating. Yet runtime depends on watts, voltage, losses, and discharge limits. This calculator combines those values into one practical estimate.
Understanding Battery Energy
Battery energy is normally found in watt hours. Watt hours show how much work the battery can deliver. A 12 volt 100 Ah battery has 1200 nominal watt hours. That does not mean all energy should be used. Lead acid batteries often need a shallower discharge. Lithium batteries usually allow deeper discharge. The calculator lets you set the safe discharge percentage.
Loads, Watts, And Losses
A load rating shows how much power a device needs. Lamps, routers, pumps, fridges, tools, and fans vary widely. Motors may also need high starting surge. Inverters lose energy while converting DC to AC. Wires, standby circuits, and controls also add small losses. These details reduce usable runtime. The calculator includes inverter efficiency and extra loss watts.
Battery Condition And Temperature
Real batteries rarely perform like new laboratory ratings. Age, weak cells, low temperature, and poor charging reduce capacity. Cold weather can lower available energy. Older batteries can sag under heavy load. Use the condition and temperature fields for realistic planning. A reserve percentage also protects the system from overuse.
Designing A Better Backup System
Start with a full list of connected devices. Add their running watts. Add surge watts for compressors, pumps, and motors. Choose a runtime target. Compare the required amp hours with your battery bank. Increase parallel capacity when runtime is too short. Increase voltage when current becomes too high. Always size cables, fuses, and breakers correctly. This tool gives estimates for planning. Final installations should follow electrical safety rules.
FAQs
What does this battery runtime calculator estimate?
It estimates battery runtime from voltage, amp hours, load watts, inverter efficiency, discharge limit, battery condition, temperature effect, and reserve capacity.
Can I use this for inverter backup systems?
Yes. Enter the AC load watts and inverter efficiency. The calculator converts the demand into estimated DC input power and runtime.
Why is usable energy lower than nominal energy?
Usable energy is reduced by discharge limits, battery age, temperature, reserve settings, and conversion losses. These factors make the result more realistic.
What is depth of discharge?
Depth of discharge means the battery percentage you plan to use. A lower value protects battery life but reduces available runtime.
Should I enter watts or amps?
Watts are preferred. If watts are unknown, enter amps and voltage. The calculator can estimate watts from current, voltage, and power factor.
Why does surge current matter?
Some devices need extra starting power. Motors, pumps, compressors, and refrigerators can briefly draw much higher power than their running watts.
Can this calculator size battery capacity?
Yes. Enter your target runtime. The calculator estimates required watt hours and amp hours for that runtime under your chosen conditions.
Is this result exact for every battery?
No. It is an estimate. Real runtime depends on battery chemistry, load shape, wiring, temperature, health, charge level, and manufacturer limits.