Special Report: 2011 Battery Buyer’s Guide
Running accessories with the engine off can result in a deeper discharge, and deep-discharge/recharge cycles are hard on battery plates. Purpose-built, deep-cycle batteries have fewer but thicker plates designed to stand up to deep cycling.
Unfortunately, while some deep-cycle batteries have enough plate surface area for engine starting, some do not.
Dual-purpose batteries, like the marine/RV model from Crown Battery, are designed to handle both engine starting and moderate deep cycling in cases where one battery has to do both jobs.
The label for any battery used for starting has to carry at least the minimum CCA rating for your truck.
Having more than the minimum rating helps because as you discharge the battery by operating accessories without the engine running, you also deplete its cranking amps.
Dual-purpose batteries are designed with plenty of plate surface area for engine cranking and the plates are tough enough to survive moderate deep cycling.
If you accidently run your battery down too far once in a while, you won’t hurt this battery as much as you would a pure cranking model.
Dual-purpose and deep-cycle batteries have two more ratings that can help you obtain the capacity you need: amp-hour (AH) and reserve capacity (RC).
The AH rating is probably a better indication of how long a battery can sustain smaller amp-draw loads like a non-amplified stereo or lights.
It tells you how many amps a new, fully charged battery can deliver at 80 degrees F, multiplied by the number of hours of use (amps x hours = amp hours), without falling below 10.5 volts.
AH are usually figured over a 20-hour period. For example, a 100 AH battery can deliver 5 amps for 20 hours. You simply add up the number of amps per hour that your accessories draw, multiply the total by the number of hours you want to run them and you come up with the AH rating you need.
Many AGM batteries, like the Deka Intimidator model, have both threaded and clamp-on posts, making it easier to wire up more accessory power cables with either type of terminal connector.
RC is a better indicator of how long a battery can run heavier loads like winches and other motorized equipment. The RC rating is the number of minutes a new, fully charged battery at 80 degrees F can carry a 25-amp load without falling below 10.5 volts.
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