by wlooper89 » Thu Feb 12, 2009 12:04 am
With a closer reading of the web information I learned that not all AGM batteries are deep cycle. AGM refers to the material between the plates that absorbs gas and allows the battery to be sealed, while the ability to deep cycle is a trade-off with engine cranking power.
To achieve high "cold cranking amps" for engine starting, many batteries have lead plates shaped like a sponge to give maximum surface area for the cranking amps. But repeated deep discharge shortens the life of the plates. They tend to crumble and end up in the bottom of the battery case.
A true deep cycle battery has solid lead plates with a flat surface. Not as many cranking amps but little tendency for the plates to crumble. Many marine batteries are a hybrid. They have a more coarse sponge shape for the plates so the cranking amps are not as high but still plenty to start the engine. The recovery from deep discharge is also OK but not as good as with a true deep cycle battery.
I was pretty much clueless when I bought my trailer battery. Looking at the battery specs now it appears I got an AGM hybrid with some deep cycle capability, but a lot of cranking amps I do not need as there is no engine for it to start. We usually camp where there is electric hookup, so maybe this battery will still last reasonably well. For the next one I may try to find an AGM battery that is true deep cycle. From a brief search on the web it appears that a battery designed for scooter, golf cart or solar power system may be good as it should be able to deep cycle and does not need engine starting capability.
Bill
PS AGM batteries, at least those like the one I have, are not totally sealed. There is a pressure relief valve to release excess gas pressure and then the valve reseals.
