[Oeva-list] AGM battery charging question (Tim Kutscha)

[David Kerzel]

Tim,
My understanding is over charging does not just turn into heat it causes the
battery to make Hydrogen and in AGM can over pressurize the battery.  If the
gas vents some of the precious electrolyte is lost forever.  Dropping from
the constant voltage part of the charging to the lower float voltage or just
ending the charge cycle with no float voltage is important for longest life.
Sounds like you are going for 100% charge. That is the thing to do if
maximum range is your goal.  If you are looking for maximum battery life
only charging to 90% and never discharging below 40% appears to double
battery life.  Everything has tradeoffs
David Kerzel
-----Original Message-----
Message: 1
Date: Thu, 25 Jun 2009 17:52:51 -0700 (PDT)
From: Tim Kutscha <tim_kutscha at yahoo.com>
Subject: [Oeva-list] AGM battery charging question
To: oeva-list at oeva.org
Message-ID: <307234.97758.qm at web110510.mail.gq1.yahoo.com>
Content-Type: text/plain; charset="us-ascii"

Hi all,

I've got a technical question about AGM batteries for you battery experts
out there.  A typical smart charging system will dump current into an  AGM
battery up to a critical point (say 14.4 volts at 25 degrees C) and then
hold that voltage until the current drops down to, say, 1 amp before
dropping to a float voltage (like 13.6 volts).  My question is:  if the
current going into the battery drops to around 1 amp, how long can I safely
hold that 14.4 volts before hurting an AGM battery?  I would think that the
current going in is so small, it would just be dissipated as waste heat.
I'm using 100Ahr Concorde Lifeline AGM batteries.  I have resistive shunt
balancers on all the batteries for balancing that kick in around 14.4 volts
depending on the ambient temperature.

Any thoughts?

Cheers,
Tim