AGM vs Wet Cell Battery

[karista]

My current Battery configuration is 3 Group 27 AGM's in Series and a separate AGM starter only Battery. The housebank voltage has slowly gone down, so in checking each Battery separately I found that one of the AGM's had gone down to 10.8V and charging it alone did not revive it, so it's a goner! My question is; do I replace this Battery with another AGM at a cost of well over $200, or do I replace it with a sealed wet cell battery at 1/3 of the cost and a better warranty than the AGM has?
Since my AGM's were only 4 years old with very little use, I question what the advantages really are to support their high initial cost.
I have a Statepower Charger and checking the charging rates for the AGM and Wet settings I find they are almost the same, the small difference I would think is negligible, thus leaving it set at the AGM setting should be OK for the sealed wet cell battery.
Any comments/opinions?

[Stu Jackson]

Bernd, Maine Sail, over on the co.com message board, and others, have reported that AGMs may not have been all they were touted to be.  Unless your reserve bank is in a location that is inaccessible requiring a sealed battery because you can't check the fluid, why bother with anything other than a wet cell?  And even then you can get sealed "maintenance free" wet cells for the reserve bank.  I have, and my reserve bank is in the regular battery tray just forward of the galley!

PS - this is wrong because it's one of Bernd's house bank batteries, not the reserve bank, please see below, thanks, Stu

[SeaFever]

Bernd,

I believe you mean you have the three batteries in parallel. You wouldn't want 36 volts on your boat, right?

Like Stu I too have to sealed wet cell batteries. I recently had to replace one of them and I replaced with the same type.

I am not familiar with the Statepower charger you have for charging your three house batteries. However, the only consideration I would think is whether your charger allows you to adjust different battery types for each of the batteries. I am not the expert but I believe the charging is slightly different for flooded and AGM. I have read a couple of places to 'not mix battery types'.

[Stu Jackson]

The very best comparison of battery charging regimens I have found is on the Balmar website in the regulator manuals.  Page 9 of the MaxCharge 612 has the tables:  http://balmar.net/PDF/2005-mc-612-manual.pdf

You can do your own comparisons on the voltages recommended.

Jim Moe also wrote a primer on different battery types in the wiki:  http://www.c34.org/wiki/index.php?title=C34_Battery_Selection  His conclusion is pretty clear.

Mixing battery types even house / reserve may not be appropriate given the different charging voltages recommended by Balmar's chart.

Since one of your house bank batteries fried, you could simply take it out and see if you can run your boat with just the two remaining for another year - depends on your energy budget and boat use.  I apologize, just realized your issue was one house bank, not the reserve (per my first post).  Don't take me long...

Because of my leg surgeries last year, and the neglect they suffered, my 2006 wet cell batteries have deteriorated and it's time for replacement.  Wet cells (serviceable) from a reputable company at a lot lower cost than West Marine is my choice.  I'll pick up either an inexpensive Sears automotive for the reserve bank or just another deep cycle from the same place I'll get my new house bank batteries (American Battery in Hayward).

Your boat, your choice.

[Mike and Joanne Stimmler]

One other thought on this issue is that if you have multiple batteries in a bank, it's not good to replace just one of them because the older ones can draw down the new one. Stu's idea is a good one,of eliminating the bad one and just running off the other two until you can replace them all or just stay with the two.
If you do wind up replacing all the house bank batteries, you may want to consider using 4- 6 volt golf cart batteries as many have done. This will give you over 400 amp hours and these generally last longer than the 12 volt deep cycle batteries.

Mike

[Ron Hill]

Bernd : Sorry to hear of your problem.  If you check I believe that the AGMs are warrantied for 5 years rather than 4 for the wet cells.

I'd replace the bad battery and wire it into BB 1 and wire the other two into BB 2.  You can wire the starting battery separately into a combiner.

Your statement of "very little use" bothers me as that little use tends to help kill any type of battery!  If you aren't really using them and don't need the AMPs, the thought of going with 2 batteries may be the way to go!!  Figure out your usage factor and then YOU"LL have to decide!!  A few thoughts

[karista]

I have replaced the one bad AGM with a sealed flooded deep cycle as Stu has done. The person at the commercial Battery Center where I bought it, convinced me that this was the best way to go. He said "I can sell you a AGM which will have 92 Amp/hr rating with a shorter warranty (1 year/3 yr prorated) or I can sell you a sealed flooded wet cell battery with a 100 amp/hr rating and higher cranking capacity and better warranty for 1/3rd the cost, the choice is yours.
The charging  voltages at the high temperature setting are exactly the same according to my Xantrex Manual for the AGM and WetCell so that will not be any issue. As the other AGM's fail I will replace them also with the sealed maintenance free flooding batteries. The cost difference makes no logical sense to me to replace them with AGM's, that have not proven to me to be any better than Flooding wetcell batteries.

[Lance Jones]

As Ron stated, look at the 6 volt alternative. When my 12 v AGMs die, that's the way I';m going to go.

[Stu Jackson]

I have replaced the one bad AGM with a sealed flooded deep cycle as Stu has done.

I may have been unclear, and see I was.  I am going to replace my entire house set of batteries, not just one.