Mobile Hills Automotive
Battery & 12V Calculators
Estimate a suitable auxiliary battery bank or check approximate state of charge from a resting voltage reading.
Calculate battery capacity
Enter your expected energy use and how long you need the battery to operate without charging.
Wh/day
days
Advanced settings
%
%
Don’t know your daily Wh?
- For each appliance: watts × hours used per day = Wh/day.
- Example: a 45W fridge running effectively 10 hours per day uses about 450Wh/day.
- Allow for cloudy days or low driving time if solar or a DC–DC charger normally replenishes the battery.
Estimate state of charge
Use a battery voltage measured at rest—not while the engine, charger or large accessories are operating.
volts
For a useful reading: switch the engine and chargers off, remove major loads and let the battery rest. Lead-acid batteries are best checked after several hours; LiFePO₄ voltage is very flat through much of its range, so a shunt/BMS reading is more reliable.
Important diagnostic limits
- A healthy-looking open-circuit voltage does not prove the battery can supply current. Use a proper load or conductance test for starting batteries.
- With the engine running, voltage is mainly showing charging-system behaviour—not battery state of charge.
- Always use the battery manufacturer’s data where available.
Need your battery or charging system tested?
Mobile service across Mount Barker and the Adelaide Hills.
General guidance only. Results are estimates and are not a substitute for inspection, electrical load analysis or manufacturer specifications.