I asked someone who works on nothing but Alternators, if they could make me an external regulator for my alternator (in my case a subaru), and they're weren't even willing to consider it. So much, for changing to a regulator that will put out 14.2 volts... 

From: Taeke <taeke.t@GMAIL.COM>
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Why AGM batts don't last as long as they should

> There is a schematic for a temp controlled or adj. VR that works with a bosch alt. Floating around the internets. cost $6.
> 
> -----Original Message-----
> From: Philip Zimmerman <philzimm1@OBERON.ARK.COM>
> Sent: Friday, June 13, 2008 12:15 AM
> 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.
> 

----- End Original Message -----