Leisure Battery Runtime Calculator
Estimate how long a leisure battery will run lights, a TV, phone chargers and other camping or motorhome appliances. Enter the battery’s Ah capacity, choose its chemistry and tick the items you use. Adjust quantities, power and running time to match your setup.
The result estimates time until your chosen battery reserve is reached. It accounts for the selected loads, starting charge, battery health and any inverter settings.
How to estimate your battery runtime
- Enter the battery bank’s capacity in Ah at its operating voltage, then choose flooded lead-acid, AGM, gel, LiFePO₄ or custom settings. Check the voltage after choosing a chemistry.
- Set your starting charge. Open the reserve and inverter settings to adjust the retained charge, battery health and inverter losses where applicable.
- Tick the appliances you plan to use. Set their quantities, watts per item and running-time percentage; add a custom appliance if needed.
- Choose whether each item uses battery/USB power or an inverter, then read the estimated runtime, average battery current and daily Ah demand.
Worked example: a 100 Ah, 12 V battery
For a fully charged 100 Ah battery with 100% assumed health and a 50% reserve, the available capacity is 100 × (100 − 50) ÷ 100 = 50 Ah. A continuous 60 W load measured at the battery draws 60 ÷ 12 = 5 A.
The simple runtime estimate is therefore 50 Ah ÷ 5 A = 10 hours. This example assumes no charging and no additional conversion losses. Actual runtime can be shorter because of temperature, battery condition, voltage changes and discharge-rate effects.
Why does battery chemistry matter?
The calculator starts with a 50% reserve for lead-acid, AGM and gel, and a 20% reserve for LiFePO₄. These are editable planning presets, not universal safe discharge limits or measured battery cut-off points. Follow your battery manufacturer’s guidance and check the settings for your own battery.
Appliance power and running time
The supplied appliance watts are illustrative starting values. Replace them with the power on the appliance label or a battery-side measurement where possible. Running time is the fraction of time the appliance draws that power: 25% means an average of 15 minutes per hour. The model averages this use rather than scheduling individual appliances.
Current is measured in amps (A); capacity and consumption over time are measured in amp-hours (Ah). A steady 1 A draw uses 1 Ah in one hour. Inverter-powered loads also include the efficiency and overhead entered in the settings.
What the estimate does not include
This calculation assumes no solar, mains or alternator charging. Battery ageing, cold conditions, high discharge rates, starting surges and inverter or battery-management cut-offs can change the result. It is a planning aid, not a battery monitor or a check of the electrical system’s power limits.
Checking your other camping supplies? Use the gas bottle calculator to estimate the LPG remaining in a bottle.