I'm looking at buying some AGMs from a fellow who has a several that he has
never used.
They are "new" still in the original packaging, however they are two years
old.
He said that he charged them and they have held a charge ever since
he charged them. I assume he meant he recently recharged they and they are
ok.
However I assume that in two years time they must have been quite dead
(fully drained) for a while.
So I have a question: If AGM batteries drain all the way down once and are
not charged for a long period, does it hurt the life span overall?
JW
> I'm looking at buying some AGMs from a fellow who has a several that he
> has
> never used.
> They are "new" still in the original packaging, however they are two
> years
> old.
> He said that he charged them and they have held a charge ever since
> he charged them. I assume he meant he recently recharged they and they
> are
> ok.
> However I assume that in two years time they must have been quite dead
> (fully drained) for a while.
> So I have a question: If AGM batteries drain all the way down once and
> are
> not charged for a long period, does it hurt the life span overall?
> JW
Draining all the way down to empty is practical for Ni-Cd battery only.
Don't do it because one of my Lead batteries was dead after I drained it
down to 0V. The old age may have something to do with it but there's no
reason for you to do this experiment.
Jonathan Wilson wrote:
> So I have a question: If AGM batteries drain all the way down once and are
> not charged for a long period, does it hurt the life span overall?
Yes, it totally screws it beyond all belief.
Look up 'sulphation' or maybe that's sulfation in American.
Some claim the worst effects can be reversed with care.
Graham
On Fri, 21 Mar 2008 04:46:04 +0000, Eeyore
>Jonathan Wilson wrote:
>> So I have a question: If AGM batteries drain all the way down once and are
>> not charged for a long period, does it hurt the life span overall?
>Yes, it totally screws it beyond all belief.
>Look up 'sulphation' or maybe that's sulfation in American.
>Some claim the worst effects can be reversed with care.
About 20 years ago we had many hundreds of 48v systems (in self
contained 19" cubicles) running on a float basis comms equipment
effectively 99% of the time the chargers fed from the mains ran the
48v equipment, depending on the equipment load the cells provided
about 24-48h backup in case of mains failure.
About 10 systems were held in long term hot standby with no external
load running with just a float charge - but at some point the
(unmonitored) supply failed and due to organisational changes no one
knew about the problem until some considerable time later, maybe 3 or
4 years. In the meantime the systems in the field were failing due to
the individual (6v) cells splitting due to manufacturing defects and
overcharging which had also caused some cells to go dry due to the
manufacturers complete lack of knowledge on charge regime, venting and
electrolyte recombination.
The cells in the systems that had been left off charge were charged
and subject to discharge tests down to 30% SOC to determine their
capacity - very surprisingly this was within a fraction of a % of
their original stated capacity so they were placed in service - with
the charging regime tweaked to hopefully avoid any further cell
failures. These spare systems, along with new ones obtained from the
original manufacturer who accepted their systems were inherently unfit
for purpose were moved on a rotation basis replacing existing systems
but like all the systems their performance was tracked until they were
eventually scrapped. In general these systems ended up having a
service life of around 10-12 years compared to the 25 claimed by the
manufacturers. If you take into account the battery racks destroyed
by split cells and acid damage the realistic life was probably nearer
5 years. The cells that had been effectively completely discharged
for an extended period showed better overall life (by capacity
measurement) than those that had been on "float" charge - albeit at a
higher voltage than the battery chemistry and construction required.
Meanwhile, as an interesting comparison, AGM cells and chargers from
another manufacturer installed in around 1980 were still functioning
and had a capacity exceeding their original design spec in around 2002
at their last test, with zero cell failures, and zero charger
failures.
The upshot is,
1) AGM cell manufacturing quality varies enormously.
2) manufacturers of cells (and chargers) very rarely, if ever, know
the correct charge voltage to use.
3) leaving cells to self discharge makes little difference to their
capacity.
4) IMHO, and that of a few others even more familiar with the
problem, only one manufacturer on the planet *really* understands AGM
recombination cells, unfortunately that independent manufacturer is
now in the hands of another corporation, if they utilise the knowledge
and expertise within that company then all well and good, if they
don't then all bets are off and AGM technology will sadly fall firmly
into the "do not touch with a bargepole" category.
--
Mike wrote:
> On Fri, 21 Mar 2008 04:46:04 +0000, Eeyore
> 4) IMHO, and that of a few others even more familiar with the
> problem, only one manufacturer on the planet *really* understands AGM
> recombination cells, unfortunately that independent manufacturer is
> now in the hands of another corporation,
What company is that?
JW
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> has
> never used.
> They are "new" still in the original packaging, however they are two
> years
> old.
> He said that he charged them and they have held a charge ever since
> he charged them. I assume he meant he recently recharged they and they
> are
> ok.
> However I assume that in two years time they must have been quite dead
> (fully drained) for a while.
> So I have a question: If AGM batteries drain all the way down once and
> are
> not charged for a long period, does it hurt the life span overall?
> JW