How long will a 12V battery run your camping gear?
Estimate battery runtime from appliance energy use, battery capacity and system losses.
Work in watt-hours rather than amp-hours alone; real-world runtime depends on loads, battery limits and charging.
Convert capacity to energy
Nominal watt-hours are approximately battery voltage multiplied by amp-hours. For example, a nominal 12.8V 100Ah battery has about 1,280Wh before manufacturer limits and losses.
Different chemistries have different usable-capacity recommendations. Check the manufacturer’s permitted depth of discharge and temperature restrictions.
Estimate daily demand
Multiply each appliance’s typical watts by the number of hours it operates daily. For compressor fridges, use a measured or published daily energy figure rather than multiplying peak watts by 24 hours.
Add lights, charging, fans, pumps and standby loads. Allow for inverter inefficiency if using 240V equipment.
Calculate an approximate runtime
Estimated days without charging = usable battery Wh divided by daily Wh consumption. This is a planning estimate, not a guarantee.
For example, 1,000Wh of usable energy divided by 500Wh per day gives roughly two days before allowing further safety margin.
Before you buy: checklist
- Nominal voltage and Ah
- Manufacturer usable-energy limits
- Daily consumption of each appliance
- Inverter and wiring losses
- Solar or alternator recharge plan
- Extra reserve for poor conditions
Frequently asked questions
Is 100Ah the same for all batteries?
No. Voltage, chemistry, discharge limits and efficiency affect usable energy.
Does a fridge run at its rated watts all day?
Usually not. Compressor fridges cycle, and actual consumption varies with conditions.