Auxiliary Battery Sizing Calculator

An auxiliary battery system is a secondary electrical system separate from your vehicle's starting battery. It powers camping equipment, lights, fridges, and other accessories without draining your main battery, ensuring you can still start your vehicle.

Check the device's data plate or manual for wattage. If only amperage is listed, multiply the amps by 12V to get watts (e.g., 4A × 12V = 48W). Many modern devices also list power consumption in their specifications.

Lead acid batteries are cheaper but heavier, with a maximum 50% depth of discharge. Lithium batteries cost more upfront but are lighter, last longer, and can be discharged up to 100%, providing more usable capacity.

Depth of discharge (DoD) determines how much of your battery's capacity you can safely use. Exceeding recommended DoD levels significantly reduces battery lifespan. Lead acid batteries should only be discharged to 50%, while lithium can go to 100%.

Yes, adding a 20-30% safety margin is recommended to account for battery aging, temperature effects, unexpected usage, and system inefficiencies. This ensures your system remains reliable over time.

No, never mix different battery types (lead acid with lithium) or different capacities in the same system. This can cause uneven charging and discharging, potentially damaging your batteries and creating safety hazards.

Runtime depends on your daily power consumption and usable battery capacity. The calculator shows your estimated runtime in days based on your inputs. Factors like temperature, battery age, and inverter efficiency can affect actual runtime.

For weekend camping, calculate your daily consumption and multiply by the number of days, then add a safety margin. A typical setup with LED lights, water pump, and phone charging might need 50-100Ah for a weekend trip.