Calculator
Example Data Table
| Battery Bank | Load | Efficiency | Discharge | Expected Use |
|---|---|---|---|---|
| 12 V, 100 Ah AGM | 100 W | 90% | 50% | Small inverter load |
| 24 V, 200 Ah lead acid | 350 W | 88% | 50% | RV lighting and fan |
| 12 V, 100 Ah lithium | 60 W | 95% | 80% | Portable fridge |
| 48 V, 400 Ah bank | 1200 W | 92% | 60% | Backup power |
Formula Used
Bank voltage = battery voltage × batteries in series.
Bank amp hours = battery capacity Ah × parallel strings.
Bank watt hours = bank voltage × bank amp hours.
Battery current = adjusted load watts ÷ bank voltage.
Peukert factor = (rated current ÷ current per string)Peukert exponent − 1.
Runtime = usable amp hours ÷ battery current.
Usable amp hours include discharge limit, temperature factor, battery health, Peukert factor, and reserve margin.
How to Use This Calculator
- Enter the amp hour rating of one battery.
- Enter the voltage of one battery.
- Add the number of series batteries and parallel strings.
- Enter the load in watts or amps.
- Add inverter efficiency for AC loads.
- Set discharge, reserve, temperature, and battery health.
- Press the calculate button to view runtime.
- Download the result as CSV or PDF when needed.
Deep Cycle Battery Runtime Guide
A deep cycle battery is made for steady energy delivery. It can support lights, pumps, inverters, tools, fridges, and small backup systems. Runtime depends on more than amp hours. The load, voltage, discharge limit, inverter loss, battery age, and temperature all matter.
Why Runtime Changes
A battery rated at 100 Ah is usually tested at a twenty hour rate. Heavy loads pull higher current. That reduces useful capacity in many lead acid batteries. This effect is called Peukert loss. Lithium batteries have a lower loss, but safe discharge limits still apply. Cold weather also lowers available capacity. Old batteries deliver less energy than new ones.
Good Inputs Give Better Results
Start with the rated amp hour value printed on the battery label. Use the same voltage that your bank uses. Add the number of series batteries and parallel strings. Series raises voltage. Parallel raises amp hour capacity. Enter the real load in watts for inverter loads. Use amps only when the current is already known at battery voltage.
Planning With Reserve
A runtime estimate should not use every stored watt hour. A reserve margin helps prevent shutdown. It also protects battery life. Flooded, AGM, and gel batteries often last longer with moderate discharge. Lithium batteries can usually allow deeper discharge. Always follow the battery maker limits.
Reading the Output
This calculator reports bank voltage, usable energy, battery current, estimated runtime, and reserve adjusted runtime. It also shows a practical recommendation. The estimate is useful for solar sheds, boats, RVs, field work, alarms, and emergency backup planning.
Safety Notes
Battery wiring must match expected current. Use correct fuses, cable size, ventilation, and terminals. Inverters can draw large surge current. Motors and compressors may need extra starting power. Runtime math does not replace a proper electrical design. It gives a clear planning estimate. Test the real system under load when reliability matters. Keep records of each test. Note battery voltage before and after use. Note the actual load and room temperature. These details make future estimates stronger. They also help spot weak batteries early. If runtime drops quickly, inspect connections, charger settings, and battery health before adding more capacity to the system and check all load ratings.
FAQs
What is a deep cycle battery?
A deep cycle battery is built to provide steady power over time. It is different from a starter battery, which gives short bursts of high current.
Why is actual runtime lower than rated capacity?
Rated capacity is measured under controlled conditions. Real loads, inverter loss, temperature, cable loss, age, and discharge limits reduce the usable runtime.
What is Peukert exponent?
Peukert exponent estimates how capacity drops under high current draw. Lead acid batteries are more affected. Lithium batteries usually have a lower exponent.
What depth of discharge should I use?
Use the limit recommended by the battery maker. Many lead acid batteries use around 50 percent. Many lithium batteries allow deeper discharge.
Should I enter watts or amps?
Enter watts for appliance or inverter loads. Enter amps only when the current is already measured or known at the battery bank voltage.
Why does inverter efficiency matter?
An inverter uses some energy while converting battery power to AC power. Lower efficiency means the battery must supply more power for the same load.
Does cold weather reduce runtime?
Yes. Cold temperatures reduce available battery capacity. The calculator applies a temperature factor to estimate this loss during runtime planning.
Can this calculator be used for lithium batteries?
Yes. Select lithium, use a low Peukert exponent, and enter the discharge limit recommended by the battery manufacturer.