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.
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Need more battery runtime?
If the calculator shows your current setup will not last long enough, these are the four most practical areas to investigate. We are linking to broad Amazon UK searches rather than claiming one product is right for every installation.
100Ah LiFePO₄ leisure batteries
Useful when you want substantially more usable capacity than a typical lead-acid battery of the same nominal Ah rating. Check charger compatibility, dimensions, BMS limits and cold-temperature charging requirements.
Browse on Amazon UK (paid link)Battery monitor with shunt
A shunt-based monitor gives a much better picture of actual charge and energy use than relying on battery voltage alone.
Browse on Amazon UK (paid link)MPPT solar charge controllers
For adding solar charging to a suitable leisure-battery system. Match the controller to your panel voltage/current, battery chemistry and overall system design.
Browse on Amazon UK (paid link)Pure sine-wave inverters
If you genuinely need 230V appliances, size the inverter for both continuous load and starting surge. A larger inverter does not create more battery capacity.
Browse on Amazon UK (paid link)Amazon search results can include products from multiple sellers and brands. Check specifications and suitability for your own electrical system before buying.
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.
Choosing a battery? Use our What size leisure battery do I need? calculator to turn your expected daily usage into a practical battery-bank target.
Checking your other camping supplies? Use the gas bottle calculator to estimate the LPG remaining in a bottle.
How to use the leisure battery runtime calculator
Enter the battery capacity and voltage, choose a realistic usable percentage for your battery type, then enter the power draw of the appliance or combined loads. For mains appliances running through an inverter, allow for inverter losses as well as the appliance’s rated wattage.
Worked example
A 12 V 100 Ah battery contains about 1,200 Wh nominally. If 80% is treated as usable and an inverter delivers about 90% of that energy to a 60 W load, the simple estimate is roughly 864 Wh ÷ 60 W = 14.4 hours. Real runtime can be shorter because battery voltage, temperature, age, inverter standby use and changing loads all matter.
Leisure battery runtime FAQs
Should I use the appliance’s watts or amps?
Use watts when possible. If you only know current, power can be estimated from volts × amps, but DC and mains-side figures should not be mixed without accounting for conversion losses.
Why is the real runtime lower than the calculator?
Common reasons include inverter losses, battery ageing, cold temperatures, cable losses, voltage cut-offs and other background loads that were not entered.
Can I use 100% of a leisure battery’s stated capacity?
Usually that is not a sensible planning assumption. The practical usable fraction depends on battery chemistry, the manufacturer’s limits and the required service life.