Example Data Table
| Setup |
Battery Bank |
Load |
Major Settings |
Approximate Runtime |
| Small backup |
12 V, 100 Ah |
500 W |
90% efficiency, 80% discharge, Peukert 1.10 |
1.24 hours |
| Medium inverter bank |
24 V, 200 Ah |
600 W |
92% efficiency, aged to 90%, temperature 95% |
4.10 hours |
| Larger storage bank |
48 V, 200 Ah |
800 W |
90% efficiency, 85% discharge, 10% safety |
7.77 hours |
Formula Used
Bank voltage = single battery voltage × series batteries.
Bank amp hours = single battery Ah × parallel strings.
Stored watt hours = bank voltage × bank amp hours.
Usable watt hours = stored Wh × discharge factor × condition factor × temperature factor.
Adjusted battery load = connected watts ÷ inverter efficiency.
Peukert factor = (rated current ÷ actual current)Peukert exponent - 1.
Runtime = usable Wh ÷ adjusted battery load × Peukert factor × safety factor.
Runtime after reserve = runtime - reserve hours.
How to Use This Calculator
Enter the total watts used by your appliance or group of loads. Add standby watts if any device stays on continuously.
Enter the voltage and amp hour rating printed on one battery. Then enter how many batteries are connected in series and parallel.
Choose whether inverter losses apply. For AC loads from an inverter, leave this set to yes. For direct DC loads, choose no.
Set depth of discharge, battery condition, temperature factor, and safety margin. Use conservative values for older batteries or important backup systems.
Press calculate. The result appears above the form. Use the CSV or PDF buttons to save the calculation.
Battery Runtime Planning
Battery runtime is not only a simple watt hour division. Real systems lose energy through inverters, wiring, heat, and battery chemistry. A useful calculator should include those losses before it gives an answer. This page estimates runtime from the load in watts, the battery voltage, and the amp hour rating. It also lets you add depth of discharge, battery age, temperature derating, safety margin, and Peukert behavior.
Why Watts Matter
A watt load tells how fast energy is being used. A 600 watt appliance uses twice the energy of a 300 watt appliance during the same time. Battery labels often show amp hours, so the calculator converts amp hours into watt hours. It multiplies volts by amp hours, then adjusts the result. This makes different battery banks easier to compare.
Losses And Limits
Inverters are never perfect. A 90 percent inverter must pull more power from the battery than the appliance receives. Lead acid batteries also lose practical capacity when current is high. Peukert adjustment estimates this effect. Lithium batteries have a smaller effect, but they still need discharge limits. Depth of discharge protects battery life. A battery used to 80 percent discharge usually lasts longer than one fully drained every cycle.
Bank Design
Series batteries raise voltage. Parallel batteries raise amp hour capacity. Four 12 volt 100 amp hour batteries can form a 48 volt 100 amp hour bank, or a 12 volt 400 amp hour bank. Both store about the same energy. The best layout depends on inverter voltage, wire size, and current limits.
Safer Use
Runtime estimates are planning values. Real results change with battery brand, temperature, age, cable length, and load pattern. Motors may surge at startup. Electronics may draw standby power. Keep a reserve for shutdown time. Check manufacturer ratings before final design. Use the output as a guide for backup systems, solar storage, field equipment, and emergency power.
Reading The Result
The final hours value shows estimated usable time after all selected factors. The table separates stored energy, usable energy, adjusted load, current draw, and reserve time. These details help you find the weak point. Lower the load, increase capacity, improve efficiency, or reduce discharge depth to improve runtime without guessing.
FAQs
1. What does battery runtime mean?
Battery runtime is the estimated time a battery bank can power a load. It depends on stored energy, connected watts, losses, discharge limits, battery age, and temperature.
2. Why does the calculator ask for watts?
Watts show how quickly the load consumes energy. A higher watt load drains the same battery faster. This makes watts the main input for runtime planning.
3. What is depth of discharge?
Depth of discharge is the percent of battery capacity you plan to use. Lower discharge can improve battery life, especially for lead acid batteries.
4. Should I include inverter efficiency?
Use inverter efficiency when powering AC appliances from batteries. The inverter consumes extra battery energy, so runtime becomes shorter than a simple watt hour estimate.
5. What Peukert exponent should I use?
Use 1.05 to 1.15 for many lithium batteries. Use 1.15 to 1.30 for many lead acid batteries. Check the battery datasheet when possible.
6. Do batteries in series increase runtime?
Series wiring raises voltage but does not raise amp hours. Stored watt hours can rise when more batteries are added, so runtime may increase through total energy.
7. Do batteries in parallel increase runtime?
Parallel wiring raises amp hour capacity. This usually increases runtime because the battery bank stores more energy at the same voltage.
8. Is the result exact?
No. It is an estimate. Real runtime depends on battery quality, age, temperature, cable losses, inverter behavior, and changing load patterns.