Rex and 4js8wh, you're both basically correct in your viewpoints. Some batteries are marketed as AGM deep cycle, but they're not a TRUE deep cycle; more of a hybrid design. I recently purchased such a battery for the 120V inverter connected to my sump pump.

BTW, Odyssey is a very respected brand, used by many boaters, RVers and solar power enthusiasts.

I've quoted the following information from: http://www.solar-electric.com/deep-c...ttery-faq.html)

Mike


Starting, Marine, or Deep-Cycle Batteries

Starting (sometimes called SLI, for starting, lighting, ignition) batteries are commonly used to start and run engines. Engine starters need a very large starting current for a very short time. Starting batteries have a large number of thin plates for maximum surface area. The plates are composed of a Lead "sponge", similar in appearance to a very fine foam sponge. This gives a very large surface area, but if deep cycled, this sponge will quickly be consumed and fall to the bottom of the cells. Automotive batteries will generally fail after 30-150 deep cycles if deep cycled, while they may last for thousands of cycles in normal starting use (2-5% discharge).

Deep Cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates - not sponge. This gives less surface area, thus less "instant" power like starting batteries need. Although these can be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge. Unfortunately, it is often impossible to tell what you are really buying in some of the discount stores or places that specialize in automotive batteries. The golf car battery is quite popular for small systems and RV's. The problem is that "golf car" refers to a size of battery case (commonly called GC-2, or T-105), not the type or construction - so the quality and construction of a golf car battery can vary considerably - ranging from the cheap off brand with thin plates up to true deep cycle brands, such as Crown, Deka, Trojan, etc. In general, you get what you pay for.

Marine batteries are usually a "hybrid", and fall between the starting and deep-cycle batteries, though a few (Rolls-Surrette and Concorde, for example) are true deep cycle. In the hybrid, the plates may be composed of Lead sponge, but it is coarser and heavier than that used in starting batteries. It is often hard to tell what you are getting in a "marine" battery, but most are a hybrid. Starting batteries are usually rated at "CCA", or cold cranking amps, or "MCA", Marine cranking amps - the same as "CA". Any battery with the capacity shown in CA or MCA may or may not be a true deep-cycle battery. It is sometimes hard to tell, as the term deep cycle is often overused - we have even seen the term "deep cycle" used in automotive starting battery advertising. CA and MCA ratings are at 32 degrees F, while CCA is at zero degree F. Unfortunately, the only positive way to tell with some batteries is to buy one and cut it open - not much of an option.

Deep Cycle Battery as a Starting Battery
There is generally no problem with this, providing that allowance is made for the lower cranking amps compared to a similar size starting battery. As a general rule, if you are going to use a true deep cycle battery (such as the Concorde SunXtender) also as a starting battery, it should be oversized about 20% compared to the existing or recommended starting battery group size to get the same cranking amps. That is about the same as replacing a group 24 with a group 31. With modern engines with fuel injection and electronic ignition, it generally takes much less battery power to crank and start them, so raw cranking amps is less important than it used to be. On the other hand, many cars, boats, and RV's are more heavily loaded with power sucking "appliances", such as megawatt stereo systems etc. that are more suited for deep cycle batteries. We have used the Concorde SunXtender AGM batteries in some of our vehicles with no problems.

It will not hurt a deep cycle battery to be used as a starting battery, but for the same size battery they cannot supply as much cranking amps as a regular starting battery and is usually much more expensive.

 

Vehicles go unused for long stretches of time (recently 3.5 months) and have aftermarket additions that remain active while the vehicle is off, getting a jump even using a self-jumper isn't practical or safe depending upon location

If the vehicle was a standard daily driver, I wouldn't need it

 

here's some information I collected during my battery evaluation


https://www.f150forum.com/f118/battery-options-321385/

 

I buy my vehicles new and keep them a long time. I have never had ANY aftermarket battery last longer than the OEM battery. Even the Motorcraft replacement batteries don't last as long as the ones directly from the factory. The OEM batteries (at least from Ford) are the best that any money can buy (even if you can't buy them....)

 

I've been using XS Power batteries for a decade now. Still have one from 8 years ago that still sits at 13 volts that gets used in a Jon boat. Expensive but great batteries especially if you're using a bunch of add on accessories or stereo equipment.