Date: Sun, 11 Jul 1999
From: "David E. Damouth" <[email protected]>
Subject: House Batteries ?

dstremme <[email protected]> sez;
>Are :
>1: Standard Automotive
>2: Deep Cycle Marine
>3: Gel Cell
>4: Absorbed Glass Mat
>batteries, preferred for the House Power applications in a Class "C" type unit?

Not a simple question! You have to state what criteria on which you base your preference. My answer would be "none of the above".

If you have room for two batteries, I'll vote for high quality golf cart batteries such as the Trojan T105 (they are 6v. and must be installed in pairs). In RV use, these have the highest amphour capacity and longest life per dollar of any battery type. That is, over a five year period, they will cost less than any other option with similar storage capacity. They are a bit narrower and taller than group 27 batteries - a problem in some installations. I have Interstate golf cart batteries, which I believe are of similar quality to the Trojans. They are still going strong after over two years of full-timing. This golf cart battery is usually rated at about 220 amphours (a pair is still 220 amphours since they are connected in series.)

You can get longer life with industrial 6 volt batteries such as the L16, at a higher initial cost and (slightly) higher lifetime cost. These are tall batteries which may not fit typical battery compartments. They also weigh 123 pounds - think about how you will handle them. They are typically 350 amphours.

You'll also hear 8D batteries recommended. These are flooded-cell batteries about twice as large and twice the capacity of a group 27 auto starting battery. A standard 8D is intended for engine starting and will have inferior performance as a house battery. There is a true deep cycle battery made in this size (West Marine carries it). It is similar to other 12v. deep cycle batteries - about a 350 cycle life.

You can get lower maintenance requirements with AGM or Gel Cell, but at a much higher cost and a lower storage capacity per pound or per cubic inch. These two types seem to have almost identical characteristics. Both of these battery types are very sensitive to overcharging, and can be permanently damaged by this kind of abuse. These are the batteries of choice if they have to be installed in unventilated living areas. They can be installed on their sides, or even upside down. If long term storage is an issue, the gel or AGM batteries will self-discharge less than any of the flooded cells - typically 3% per month, compared to 6.5% per month for flooded batteries. This means that you could safely leave gel or AGM batteries in your RV all winter (disconnected of course) without worrying about their freezing or becoming fully discharged. Flooded batteries should be checked, and probably re-charged every couple of months while being stored.

Standard automotive batteries are by far the *worst* choice for house batteries. Over the long haul, they will cost 20 times as much as golf cart batteries.

"Marine deep cycle" is a meaningless term, since the term is used for slightly modified automotive cranking batteries as well as for true deep cycle batteries. You should be very nervous about batteries labeled this way, unless you read and understand the detailed specification. The best 12v. marine deep cycle batteries (for example the West Marine Seavolt, manufactured by Trojan) are nearly equal to golf cart batteries in terms of amphours per pound or per cubic inch. But typically, the life of the 12v deep cycle battery is 350 cycles, the golf cart 700 cycles, and the L16 1000 cycles..


Dave and Helen Damouth