What should I look for when buying Deep Cycle batteries?

The most essential consideration in buying a Deep Cycle battery is first to make sure the battery you are considering is a “True or Real” deep cycle battery. Once you have determined that the battery type is correct, ensure the Ampere-Hour or Reserve Capacity rating of the battery will meet or exceed your requirements. Most deep cycle batteries are rated in discharge rates of 100 hours, 20 hours, 10 hours, 8 hours or 5 hours, and/or reserve capacity minutes.

Reserve Capacity (RC) is the number of minutes a fully charged lead acid battery at 80° F (26.7°

  1. can be discharged at 25 amps before the voltage falls below 1.75 volts per cell (100% DOD). To convert RC to Ampere-Hours at the 25 amp rate, multiply RC by.4167.

It is better to have more ampere-hours (or RC) because, within the same battery type, footprint or industry group size, the battery with higher ampere-hours (or RC) will tend to deliver longer discharge times. It is also essential to know the battery's electrochemical design. A 100 ampere-hour battery of a certain dimension designed for UPS applications may deliver more initial runtime than a Traction or Deep Cycle battery of the same dimension. Still, it will not provide the life or number of cycles that the Traction or Deep Cycle battery will. Contrary to popular belief, battery weight (while important) is “not” the perfect indication of the quality of one battery to another. It is almost certain if two batteries of the same dimension are weighed.

- one battery designed for UPS service and the other battery designed for Deep Cycle service- the UPS battery should weigh more. Be sure you understand what you are buying!

The “Battery Council International” manual BCIS-05 Rev. Dec02 provides some guidance with amp hour capacity relationships when comparing battery design for the same service application. In it, they state that “for guidance in establishing rates, ampere-hour capacity relationships are approximate”:

20 hour


3 hour


6 hour


2 hour


5 hour


1 hour


4 hour




Finally, the available space and weight restrictions will have to be considered when determining the appropriate deep cycle battery.