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.

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Taeke
Sent: Thursday, June 12, 2008 5:22 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Battery Woes/Choice

Agm are superior in charging eff. And in speed of acceptance in bulk charge.
And in rate of self discharge.  Since it costs money and time to put amps
back in the battery and they are rated for 80 % discharge not 50 they do
have some compelling advantages. If the price was even id certainly go with
AGM.

 Plenty of people use agm for solar and marine ... Just not tiny oddeseys.

-----Original Message-----
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sent: Tuesday, June 10, 2008 10:03 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Battery Woes/Choice

Flooded or wet or normal lead acid batteries come in many varieties. Most
golf cart batteries are of a flooded design. So are most forklift
batteries.

So according to the advertisements AGM batteries can withstand deep
discharges. Good for 150 to 300 cycles. Wow! A good flooded forklift
battery is designed and sold for 5 years at 5 cycles per week. That's
1,300 cycles.
I just got a van towed in with 3 Odysseys. All three just tested as junk.
Were installed 04/06.

The only real advantage of AGM is spill resistance and reduced off
gassing. Once they vent the lost electrolyte can't be replaced. They do
dry out and they can't be equalized or de-sulfated without some damage.
The benefits are more hype than reality.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Troy
Sent: Sunday, June 08, 2008 2:56 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Battery Woes/Choice

The less a battery is drained/discharged the longer it will last. Strictly
speaking, flooded batteries are not designed for repeated deep discharges,
so when used in this manner, they fail prematurely. Frank was acutely
aware
of this fact, so chose to buy from a place that had a great warranty
service, as did I.

AGM batteries, on the other hand, are designed for repeated deep
discharges,
but require a sustained voltage of over 14 V to charge them fully, and
most
alternators will not do this (at least without modification). So, yes it
is
a good thing to have lots of reserve capacity.

The only thing I've read about capacity of AGM's, and perhaps somebody
else
can confirm this, is they require 10 or 12 deep discharges before they
reach
their full capacity. I've not run enough tests on one to know.

Take a look at: http://www.vanagonwiki.net/index.php/Solar for some good
reading about batteries. Thanks to Mr. Squirrel for passing this link
along
to me.

Troy

----- Original Message -----
From: "Taeke" <taeke.t@gmail.com>
To: "Troy" <colorworks@gci.net>; <vanagon@GERRY.VANAGON.COM>
Sent: Sunday, June 08, 2008 2:37 AM
Subject: RE: Battery Woes/Choice

Is it good to have too much rc/size? Especially if it means it has thinner
plates.