Deep-Cycle Battery Calculator

Calculate your estimated daily Ah power requirement using the guide below.

Please Note: This is intended as a guide only. Data is subject to change without notice. R&J Batteries Pty Ltd exercise great care in the compilation of the data but bear no liability for any error or omission. Please confirm your Ah power requirements by calling your closest R&J Batteries Pty Ltd store or distributor – Call 1300 769 282.

Appliances/devices used
Watts – If watts are known enter watts and Amps are automatically calculated.
Amps – If watts are not known for 12v devices they can be manually added (this will delete the auto calculation)
Usage – Enter expected hours and mins per day
Watt Hours per day is automatically calculated.
Amp Hours per day is automatically calculated.

Batteries available
Enter different battery configurations 

Days of average usage
The number of days you can expect from a full charge. No solar input or Alternator input is included here.

Calculating Battery Size for Deep-Cycle Power Supply – R&J Batteries

  1. Calculate the estimated daily power requirement in Ah using the guide above (fill in your own power requirement details), or the actual power requirements of your accessories if known.
  2. Multiply the daily power requirement in Ah x number of days between re-charges (usually 1 to 3 days) for total power capacity requirement.
  3. Choose a battery / batteries with double the actual Ah requirement for improved battery life and reliability. (Eg:- 20Ah daily x 3days = 60Ah – choose a 120Ah battery)
  4. If using an inverter add 10% to 20% to Ah usage to allow for inverter efficiency rate (usually between 80% – 90% efficiency for Pure Sine-Wave inverter).
  5. Ensure sufficient re-charging capacity (wind, solar, battery charger, etc.) to fully charge battery to 100% between cycles.
  6. Failure to fully recharge battery between cycles (before re-using) will shorten battery life.
  7. Deeper discharges between cycles will shorten battery life.

Power Requirement Guide Calculator EXAMPLE:
Deep-Cycle Power Calculator example



















Using the above calculator as an example. Daily power consumption is 130AH

Total battery capacity requirement would be 250Ah if charged daily, and around 750Ah if charged once every three days (allowing for 50% DOD).

Typical 120Ah deep-cycle battery can reliably supply around 750 Watt-Hours if charged daily and only around 250 Watt-Hours daily if charged once every three days.

Solution to this equation – reduce consumption by using appliances sparingly, add more batteries (and re-charging capability), and / or supplement power supply with solar panels.