Yes, it's a problem due to higher internal resistance of the AGM and Gel
design.  Marine alternators are set to the proper 14.4 volts needed for AGM
charging, and are much more robust compared to car alternators.  I'll have
to do more research on car alternators to see if there is any way to get the
14.4 needed.  But maybe just another specific charger is the simplest way to
deal with this.

Stuart

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Philip Zimmerman
Sent: Thursday, June 12, 2008 9:15 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Why AGM batts don't last as long as they should

Good to hear your report of this confirmation Stuart!
Anytime I hear of a Vanagon with a dead AGM or two, I'm curious to know
what is the charging voltage at the battery terminals? If anything less
than the "magic" number of 14.2 or so, an AGM is going to perform
poorly or less than optimal.

I further concur with your suggestion for utilizing a Charger
specifically designed for AGM's on a routine basis. Any battery (let
alone an AGM) will perform better following a good full three-stage
charge from a 110VAC Charger. Gotta keep those electrons stirred-up....

Phil Z.
Campbell River, BC
-----------------------

Date:    Thu, 12 Jun 2008 11:37:31 -0700
From:    Stuart MacMillan <macgroup@COMCAST.NET>

After talking to a few marine electrical experts, it seems the problem
with
AGM's in cars is the alternator voltage is too low.  You need 14.2
volts to
fully charge a discharged AGM, and most alternators put out about 13 to
13.7
volts, depending on load, which is fine for flooded standard and deep
cycle
batteries, but never fully charges an AGM.  So, either find someone who
can
tweak the alternator output, or buy a charger specifically designed for
AGM
& Gel and use it at least once a week.