Robin2:
As I said earlier, in my opinion the Ah capacities of lead acid batteries are grossly exaggerated - perhaps twice what they really are.
I could not open your links to the batteries.
Starter batteries are specially designed to give a huge current for a few seconds until an engine starts. I presume you can get sealed starter batteries but they would not be suitable for sustained output or more than a few moderately deep discharges.
I use my un-sealed lead acid batteries 24/7.
...R
Yeah like I said that's why it's super important to get a deep cycle battery, usually labeled as a Marine or RV battery. Lead Acid batteries are categorized as SLI(Starting, Lighting, and Ignition). They can then be broken down into two more categories, starter batteries and deep cycle batteries.
Your starter batteries that you mention, you are absolutely correct. They are designed to meet the current requirements of a starter, and then be charged right back up via an alternator or a stator. While some manufacturers do put an AH rating on the battery, you really should ignore that. They should have a CCA rating on it, which stands for Cold Cranking Amps. There's a relationship between CCA and true Amps the battery can deliver, which I cannot remember off the top of my head.
The reason they don't last as long in a deep discharge application is because of a process that we called sulphation. Basically, when a battery gets below 80% of it's charge, the sulphur in the sulphuric acid would begin to separate from the acid and form on the lead plates. The lead plates have holes in them for electron flow, and the sulphur buildup would start to restrict electron flow. The analogy that we liked to use was that it's similar to plaque buildup in arteries before somebody has a heart attack.
The reason that deep cycle batteries are required for this kind of application is two fold. Deep cycle batteries are built with thicker plates, to help negate the effects of sulphation. Secondly, the plates were coated in a solution that would slow down the actual effect of sulphation. Allowing the battery to be dropped below the 80% charge threshold. These batteries also sacrifice some of the CCA capabilities of their starter counterparts.
The sealed lead acids that I linked to(one was a 12V, 14AH VRLA, the other a 12V, 35AH VRLA) are what are known as AGM(absorbed glass matting). They have a fiberglass matting that soaks up the electrolyte and creates some benefits that way. Some people call them gel cells,those people are wrong, they are almost always AGM batteries(there are very few, very specific markets for true gel batteries). All AGM have some inherent properties of a deep cycle battery, and in fact the majority of their applications are for standby power(such as this), typically in exit lights, fish finders, powerwheels toys, and actually the two I listed are commonly used for mobility scooters for those with disabilities.
The starter batteries that you said will die after a few deep discharges?You're absolutely correct. It's the equivalent of leaving your headlights on over night multiple times. Very few car batteries will handle that(the ones that will are AGMs).
Again, this is all knowledge and experience I've gained after working for four years as a technician/salesman at a store that specialized in batteries.
