Free battery sizing tool

Use this free battery size calculator to estimate the right battery Ah, Wh, runtime, and charger range for RV fridges, toys, CPAP machines, lights, trolling motors, inverters, and small 12V setups.

Find the right battery size faster. Start with device, watts, and runtime. Advanced users can adjust battery chemistry, usable capacity, buffer, duty cycle, and inverter efficiency.

Enter your setup

Choose the closest option. The watts field will auto-fill, but you can change it.

Look for W on the label, charger brick, or manual.

How many hours should the battery run the device?

Advanced settings

Defaults are already set for most shoppers. Change these only if you know your setup.


Recommended battery size

Waiting for input

Choose a device, enter watts, and add runtime to see your battery estimate.

Minimum Not calculated yet
Recommended Not calculated yet
Long-runtime option Not calculated yet
Energy estimate Not calculated yet
Suggested charger range Not calculated yet
Estimated charge time Not calculated yet
Formula used Not calculated yet
Your battery recommendation will appear here as you fill out the calculator.

Recommended Mach1 options

Recommended Mach1 options will appear after calculation.


This free battery calculator gives an estimate, not a compatibility guarantee. Always confirm voltage, chemistry, dimensions, connector type, charger output, and device manual before buying or upgrading a battery.