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Marine/RV Battery Load Calculator

by Tim Allen

You may change any value to suit your needs and match your system. Make sure that if a system is checked, that you have entered Amps and Hours per Day for that system. If the system is unchecked, the Amps and Hours per Day will be ignored.

Helpful Hint: Try putting a negative Amps number in the "Other" system to see what happens while a charging source is operating (such as solar panels or a main engine). This is how you can keep your battery bank small and still run a heavy inverter load.

Click "Calculate" when you are ready.

Use these buttons to preload typical daily values for current draw and time used:
System In use Amps Avg Hrs per Day Amp-Hrs per Day
Refrigerator
Bilge Pump
Fresh Water Pump
VHF Radio
SSB Radio
Depth/Fish Finder
GPS/Chartplotter
Radar
Autopilot
Nav Instruments
Running Lights
Bilge Blower
Windshield Wiper
Searchlight
Engine Instr.
System In use Amps Avg Hrs per Day Amp-Hrs per Day
Anchor Light
Cabin Lights (1 Amp per 10W bulb)
Cabin Fans (0.5 Amp per Fan)
Laptop Computer
Small TV
Large TV
DVD Player
Satellite Receiver
Microwave Oven
Coffee Maker
Watermaker / Desalinator
Other (Amps Negative for Charging Source)
Analysis Results
Click Here to Analyze ->
Net Daily Demand on Battery Bank:
† Peak Amps: † Peak Watts:
Amp-Hours per Day:
†† Recommended Minimum Battery Bank Size
Battery Type Wet Gel AGM
Bank Size (Amp-Hrs)
Max Charge Rate (Amps)
††† ABYC Min. (Amp-Hrs)

† Peak Amps and Peak Watts assumes that all loads (and charging sources) are on at the same time. All amp loads are based on 12 volts DC, and inverter efficiency of 90%.

†† The recommended battery bank size is based on either the Peak Amps (maximum current load) or Amp-Hours per Day (based on 50% max. discharge), whichever requires the larger battery bank. See our article Battery Bank Sizing for Your Inverter for details about the battery type.

††† The ABYC Min. is based on running left-column loads (Full-Time Loads and Loads Under Way) without a charging source for 1.5 hours, resulting in COMPLETELY DEAD batteries (Per ABYC E-11.6.1.1.3).

As you can see from experimenting with different loads, the battery type only comes into consideration when the Peak Amps is significant. This is due to the limitations of the various battery types. If the recommended battery bank size seems excessive, it may be due to the Peak Amps. Try unchecking one of the high amp draw items and recalculate.