In sci.electronics.repair on 21 May 2005 20:14:08 -0700
posted:

Is it possible to resurrect a lead acid battery from the dead?

I have an old 12 volt automobile battery that was stored for
sometime in a discharged state. The battery voltage read around
6 volts in the discharged state. I charged it at 1 amp for 10 hours and
then tested the capacity using a automotive tail light drawing 1.3
amps. The battery voltage fell from 12.5 volts to around 9 volts within
1.5 hours indicating the capacity was not too much.

When I again recharged the battery, it sustained the load for
a longer period indicating the capacity had increased to
around 5 amp hours.

I'm wondering if cycling the battery over several charge and
discharge cycles will improve the capacity?

This charge and discharge cycling seems to improve the capacity
for a couple cycles, how much improvement should I expect from
several charge and discharge dycles?

-Bill

Make sure you have adequate water in each cell, and use steam
distilled water. It's for sale at the supermarket in gallon bottles.
Also useful in steam irons. (although my plastic bottle started
leaking after 5 or 10 years.) The cell is full when the water level
is high enough that it reaches the bottom of the circular tube through
which one fills the battery. One can see that this is the case when
he sees the miniscus in a circle around the bottom of the tube. When
the level is lower, there is a miniscus, but it is along the edges of
the much larger rectangle that is the cross section of a cell *below*
the filler tube. In other words, when you can see the miniscus, the
battery cell is sufficiently full. Don't fill much more than that.

Though there are some sealed autobatteries I think, most of them now
are designed to look like they are sealed. That is, they don't have
the 6 soda-pop-bottle top caps that batteries used to have, one for
each cell. Instead there are 2 flat panels that pry off, each with
three caps molded to the bottom. I think there is usually a 2 or 3
inch, narrow slot somewhere along the edge that indicates the cap
comes off, and is a good place to pry, but I'm not sure how obvious it
is in all models.


i HAVEN'T paid too much attention lately, but when I did, everything I
ever heard was that one had to charge a lead acid battery slowly to
get the best result.

If one charges too fast, the lead in solution gets deposited back on
the lead plate before the lead sulfate** can dissolve. The result is
what is called spongey lead. I guess one problem that results from
this is that the sulfate radicals are no longer dissolved and
therefore there is not as much H2SO4.

So a one amp charger is very good. And slower would be better I
guess, but one would have to do something additional to make it
slower. When I ran my battery down to the ground, unintentionally but
for reasons I forget right now (leaving the lights on?) it would take
about 24 hours to recharge it with a one amp charger. (I guess at 50
milliamps it would take about 20 days, n'est pas?)

When I got a jump and had to go somewhere and was therefore going to
recharge the battery while driving, I kept the heater fan on high and
the headlights on to slow the charging rate, but I probably didn't
slow it enough.


Charging the battery tends to emit hydrogen through the vents, which
is why people are warned against sparks and to have adequate
ventilation, and I already mentioned the loss of sulfate radicals, the
other half of sulfuric acid. Yet, I've also read not to add more
acid, since by the theory that goes with that, only water is lost from
the battery. The two seem to contradict each other.


**PbSO4, I think it is, but maybe it was lead oxide (PbO2),

What makes lead acid batteries rechargeable is that the products of
electrical generation remain either in solution or soluable. In, for
example, carbon zinc flashlight batteries, this is not the case.

However, not all gets redissolved, and there is an empty inch or two
at the bottom of batteries where chunks of lead compounds, or detached
lead can settle. For this purpose, the more empty space the better,
because I think the most common cause of cell shorting is that the
level of junk in the bottom gets high enough to touch two consecutive
plates, or two other plates that should not be connected, except
through the acid solution. OTOH, the more empty space at the bottom,
either the bigger the battery and the more acid needed, or the smaller
the plates and the lower the maximum output per time.

Meirman
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