From the esteemed Mr. Haynes pointer, a relevant chart.
http://batterytender.com/images/largebasics3.gif

Still more to come on this.

On 6/19/08, Al Knoll <anasasi@gmail.com> wrote:
> It is a general consensus that AGM batteries do not do well when
> charging directly from an alternator.  The powerstream bc1212-15 is a
> dc to dc charger that incorporates multi stage charging it it's design
> and may solve the problem.  Rocket J. notes that this device does well
> charging his Trojan brand house battery.
>
> More to come on this.
>
> On 6/19/08, Frank Condelli <RAlanen@aol.com> wrote:
> > In a message dated 18/06/2008 2:03:29 P.M. Central Standard Time,
> > LISTSERV@GERRY.VANAGON.COM writes:
> >
> > I have  an optima yellow top that never seemed to get charged properly
> > from the  alternator.
> >
> >
> >
> >
> >        EXACTLY, I've toasted at  least three of those EXPEN$IVE Optimas
> > before giving up on them.  They are  JUNK to put it mildly.  Waste of $$$ in my
> > humble opinion !!!!!
> >
> > Cheers,
> >
> > Frank  Condelli
> > Almonte, Ontario, Canada
> > '87 Westy & Lionel Trains (_Collection for sale_
> > (http://members.aol.com/Fkc43/trainsal.htm) )
> > _Frank Condelli &  Associates_ (http://members.aol.com/Fkc43/busindex.html)
> > - Vanagon/Vanagon Westfalia Service in the Ottawa Valley
> > _Vanagon Stainless Steel Exhaust  Systems_
> > (http://members.aol.com/Fkc43/exhaust.htm)
> > _BusFusion_ (http://members.aol.com/BusFusion/bfhome.htm)  a VW Camper
> > camping event, Almonte, ON, June 12 ~ 15,  2008
> >
>