On Jun 15, 9:46 am, Salomon Fringe wrote:
...If you use a main engine or a generator
to charge then I think AGM or gel are out of the question.

And you believe this because...? I and many others have gotten many
years of outstanding service from AGMs used in exactly this way. I've
got nothing against regular old flooded batteries. They're certainly
the best in terms of capacity per monetary unit or capacity per weight
for lead acid. But the article you're quoting is being wildly, even
absurdly unfair in its comparison of the types of lead acid
batteries. He gives AGMs a particularly bad rap by asserting that
they are essentially the same thing as a "maintenance free" starting
battery. His argument seems to be "well, they've got thin plates and
you can't add water to them so they must outgas like mad if you charge
them fast and the plates must fail quickly because they are thin." Of
course, if that were true AGMs would die quickly in normal use. Yet,
I and many other folks, have AGMs that have lasted for 8+ years
despite being deep cycled and charged at significantly faster rates
than flooded cells. How can that be? The answer is that the author
of your article either doesn't know the differences between an AGM and
a cheap maintence free starting battery or is being intentionally
misleading.

As far as I know all AGMs are "valve regulated". Certainly all the
major players are. Under normal charging they recombine virtually all
gas. While massive overcharging will cause them to vent, modest
amounts of over voltage will not hurt them noticeably. Indeed, all of
the manufactures that I've looked at recommend periodically equalizing
them. Generally you can put all the amps you've go into them as long
as you regulate the voltage (max between 14.0 and 14.6 depending on
the temperature and the particular battery). Even so regulated their
acceptance rates are higher than deep cycle flooded batteries and
charge times are quicker.

AGMs do have thin plates. But, those plates are packed tightly into
the glass mat and physically very well supported. So, they are less
prone to physical failure than the thin plates in flooded starting
batteries that need to be largely self-supporting. And, at the same
time, they have more surface area than flooded deep cell batteries.
The net result is that AGMs have very low internal resistance compared
to other deep cycle batteries and are more durable. Low resistance
also reduces gassing.
....
If you read the article then you will also have read that if you are
willing to use 'reasonable charging rates' (=slow charging), standard
lead-acid is 'maintenance free' just like AGM and gel.
But AGM and gel are much more expensive.

I've read the article. It is total BS. AGMs are not gels or cheap
sealed starting batteries. All his conclusions follow from a false
assumption and no evidence for the conclusions is provided.

-- Tom.