Re: Combining battery question.

On Thu, 12 May 2005 18:48:49 +0100, "Dave Plowman (News)"
<dave@xxxxxxxxxxxxxxx> wrote:

>In article <11874ihki17pa3a@xxxxxxxxxxxxxxxxxx>,
> sofie <sofie@xxxxxxxxxx> wrote:
>> Absolutely NOT a problem to charge lead acid (gel-cell) batteries in
>> parallel ....
>> ...this is done ALL THE TIME with automotive and RV/Trailer batteries.
>
>Gel cell and lead acid ain't the same - and you don't get gel cell in cars
>as a rule.
>
>SLA - sealed lead acid - which use a gel as the electrolyte - should be
>charged with a maximum voltage of 13.8. They can't gas in the same way as
>a liquid electrolyte type can, so mustn't be overcharged.

Agreed. Charging gel-cells at over rated voltage kills the capacity.
The battery will still have proper voltage, but if you do a capacity
test, it will be drastically less than rated. We see this all the
time on ATC-601's. Aircraft mechanics are told to keep equipment on
chargers at all times, which is fine for old NiCd packs, but these
charge at 14 volts and constanly come in with ruined packs. They
won't last more than 5 minutes at rated capacity. I've been told that
the cause is because they can't "vent", as you say. They seem to work
perfectly as a replacement for lead-acid, as in they charge in exactly
the same manner, but they do lose their capacity if charged at too
high a voltage too often. As Daniel Sofie says, they put them in dirt
bikes, which makes sense. They charging system charges the batteries
just as it should, but I can guarentee that it won't last as long as a
lead acid would in its place if it wasn't vibrated and jarred to
death. The capacity loss is just an acceptable sacrifice for no
battery acid spilling. Possibly a bold statement, just my thoughts.
I bet the gel-cells still last at least a year in that situation, but
they probably have to be replaced prematurely due to capacity loss.
But, there is no perfect battery pack, and gel-cells are definantely
nice.
Steve
.

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