How do I compare battery technologies to make an informed buying decision?

Discover has made available the largest range of AGM and GEL Semi-Traction (Industrial deep-cycle), deep-cycle (and high-cycle AGM, AGM SVR and GEL product lines worldwide! This means you have several sizes and performance options when making your purchase decision. First, consider the following:

  • Do you have any size restrictions (Height, total W x L area available)
  • Do you have multiple areas available for batteries? If so, how far apart are they, and are they similar in area?
  • Is the area hard to get to, or will it be easy to install heavy batteries?
  • Do you have weight restrictions? Both on a per-battery basis and as a total installation.
  • Will the installed batteries be easy to service? If not, DO NOT consider Flooded types!
  • Does a dedicated exhaust fan service the installation area? If not, DO NOT consider Flooded types!
  • What type of battery(s) are you using now?
  • What type of charging system do you have?

With these questions answered, you are now ready to consider your options. Make sure you have read and understand the sections on How do I increase the capacity of my battery and system?

What should I look for when buying deep-cycle batteries?

The 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, make sure 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°C) 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 electrochemical battery design. A 100 ampere-hour battery of a particular 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 necessary) is “not” the perfect indication of the quality of one battery to another. It is almost certain that 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 125%
  • 3 hour 82%
  • 6 hour 100%
  • 2 hour 72%
  • 5 hour 95%
  • 1 hour 55%
  • 4 hour 89%

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