12V Deep Cycle Batteries

[Phil N Barb Rodriguez]

I had planned to buy new batteries today for our PT. I picked up 4, 6V deep cycle batteries at Costco. The only 12V batteries they had for my chassis were the DEEP CYCLE type. They were labeled "Starting Battery" for boats and Rv's.

Having heard that the chassis batteries should NOT be the deep cycle type would you guys please post any pros and cons of using 12v deep cycle batteries for engine starting batteries.

Thanks..

[Edward Buker]

Phil,

There are marine batteries that are called deep cycle type that are a compromise design. When they say that these are starting batteries for boats and RVs they are either the compromise design or not really deep cycle batteries at all. I would think that they would be fine for the job you are looking at. Have them look up the cold cranking amps for these "starting" battreries and also a standard truck type starting battery (same battery number) and see if they are comparable. This becomes less important if you never reside in a cold climate.

Later Ed

[Gerald Farris]

Phil,
Ed is right about the batteries not really being a deep cycle batteries if they can produce enough cold cranking amps (CCA) to be classed as a starting battery. Sometimes a deep cycle battery is used as a starting battery if the battery is large enough or if the engine is small enough, but they do not directly interchange.

The difference between a true deep cycle battery and a cranking battery is in the design of the battery plates. A deep cycle lead/acid battery has solid lead plates, and therefore it has minimal surface area for each plate. A cranking battery has plates that resemble a lead sponge, and therefore they have many times more surface area than a deep cycle plate. Since the surface of the plate is where the charge is, a cranking battery has the potential to deliver a lot more amps when needed to power a starter motor.

The important thing to look for in a cranking battery is the CCA rating. Without an adequate CCA rating your engine will not turn fast enough to start especially in cold weather.

Gerald