We use lead acid batteries in a product we manufacture. A few of the
batteries were left in our warehouse for over a year without charging. When
we tried to use one of them, it did not have any capacity. We contacted the
battery manufacturer's engineering department and they gave us a fix for
rejuvenating a battery that had sulfated. The fix is to charge the battery
with a constant current of C/20 for 24 hours. A 5 amp hour battery would be
charged at 5/20 or .25amp. It must be a true constant current that allows
the voltage to rise above the normal charge voltage of about 2.5 volts/per
cell. If the battery voltage is monitored during the charge it will rise to
around 3 volts per cell and when the battery is de-sulfated it will start to
drop similar to a fully charged nicad. We were told that we don't have to
monitor the voltage because a 24 hour charge would be enough.
I designed a circuit to perform the constant current charge but I have not
tried it yet.
Bill Groft
Newark, Delaware
----- Original Message -----
From: "Andrew E. Mileski" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Wednesday, January 10, 2001 4:44 PM
Subject: Re: [RCSE] Lead Acid Shelf Life
> Bill Swingle wrote:
> >
> > Let's say you've bought an extra 12V lead acid battery. You don't expect
to
> > use it for quite a while. If the battery is brand new, you've not
charged
> > it nor connected any loads to it; what's the shelf life?
>
> If it is left to self-discharge, it will sulphate :(
>
> I have two identical gell batteries. I kept one charged, and
> let the other drop to about 8V over a period of about 4 years.
> Besides being very hard to charge at first, it doesn't hold a
> charge as long as the constantly charged battery. This means
> it is sulphated (lead sulphate has crystalized on the plates),
> and has permanently lost capacity.
>
> You need to "float" the batteries (keep them from discharging).
> I've used a 9V adaptor that outputs 14.5V no-load to keep the
> good battery charged. The average voltage maintained is around
> 13.4V - they battery is speced for 13.8V float.
>
> The batteries should last a very LONG time on float.
>
> --
> Andrew E. Mileski
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