Hi Roy
On (18 Aug 96) Roy J. Tellason wrote to Alec Cameron...
And here is my answer to first message, before I read the second:
 AC> On what basis do you decide to retire an aged battery? If you 
 AC> discharge test it before condemning it, what test preparation 
 AC> do you first undertake?
 RJ> I would not get rid of one unless there were a shorted cell,  or a bad
 RJ> connection inside the battery which prevented any power drain (a 
condition
 RJ> I've encountered more and more frequently over the years).
A problem that I come across, is self drainage ie standby loss. The text 
ooks
used to put this at 1 or 2 % daily. Some cells seem to fade very much faster
and I suppose this might be the "mud" at cell bottom bridging the plates. And
not all of it easy to see even with transparent cases.
 AC> Highly- regulated *should* mean, that the output is exactly 
 AC> matched to the needs of the battery ie fast recovery when flat.
 RJ> One would hope so.  I wonder how you'd get a charger to determine 
hether
 RJ> a battery was either severely discharged or had a shorted cell,  though?
I suspect that some advanced chargers in generating stations and submarines,
have individual cell monitoring and/or measure or infer the cell internal
resistance by assessing dI/dV ie the cell conductance. At a generating 
tation
I worked in we had a few single cell chargers, so that in- service diagnosis
and correction was possible on individual cells weighing several 
hundredweight.
 RJ> ..................................  I can't quite see the sense of 
eally
 RJ> pushing a battery quite hard.  It would appear that a long,  slow charge
 RJ> would tend to let things happen in there a lot more evenly,  too.
A hefty charge on a cool battery has two advantages I can think of- rapid
return of the battery to its desired state of readiness, and compensation for
internal [series] voltage drops. The resistance of internal busses is
significant. Some are of copper clad with lead! Not a well known fact.
Resistive internals, results in full charge being acquired near the cell
terminals, before it "penetrates" in to the larger amounts of more distant
plates. Important I think with foil constructed cells eg nicads.
 RJ> One of the things that makes it hard to figure some of this stuff is 
hat
 RJ> a lot of the batteries sold for RV/Trolling use aren't rated in 
amp-hours,
 RJ>  but rather in "reserve minutes",  which is how long you'd get to run it
 RJ> at a specified temperature (usually 80 F) and with a specified draw 
most
 RJ> often 25 amps).
The battery specs in OZ are also puzzling, we no longer rate in amp hours or
plates per cell. The rated data here is now CCA- Cold Cranking Amps. For your
2 litre car you might use a 250 CCA and for your V8 you go for a 500 CCA, and
so on.  Me, I just go to K-MArt and buy the largest battery that can be 
itted
in the engine bay.
 AC> BUT if you are ripping 5 amps into a 10 amp hour battery then 
 AC> this might strip active material from the plates and also 
 AC> concentrate the electrolyte, both are harmful results.
 RJ> Removing active material from the plates?  Isn't that a normal part of 
the
 RJ> process,  that some material is going to flake off the plates over the
 RJ> life of a battery?
Severe vibration, excessive charging especially of a "full" battery are
aggressive in removing active material.
                                      
  And I don't understand your comment here about
 RJ> concentrating the electrolyte,  as that's one of the usual things that
 RJ> happens when you charge a lead-acid battery!
It's not the concentrated fluid itself that is harmful, but the reason it 
ets
that way ie the electrolysing of the acid into gases. With a diminished 
olume
of [concentrated] fluid, areas of plate are exposed and dried and these are
then lost as storage areas.
 AC> Deep discharge [standby power] is very wearing and such 
 AC> batteries are not expected to have long lifetimes.
 RJ> Actually,  it's not the discharge that does it but the leaving of a
 RJ> battery in a discharged condition -- when you do so,  you end up with 
lead
 RJ> sulfate crystals on the positive plates,  and those don't usually 
dissolve
 RJ> with a charge put back in.  You've therefore lost significant plate 
ea.
I think you have missed something. Yes, a prolonged neglect of a discharge
battery will damage it irrespective of whether it is designed for "floating"
fully charged, or for regular full discharge as with a wheelchair or golf
cart.
But if you try and use an auto starting battery in golf cart service with
daily full charge/ recharge, you will very soon retire it as it has lost
storage ability due to the shedding of active material, and some corrosion of
internal structure. I don't know how significant the corrosion is, but I have
sure seen some very sick post mortems! With daily charge/ full discharge 
here
is no chance for sulphation to occur.
                                     
 RJ> This is why letting a battery sit around for a real long time and then
 RJ> charging it up doesn't usually work,  you end up with a charge but no 
real
 RJ> power behind it for starting applications.
A text book I read, not recent, said that for a profoundly sulphated battery
you should drain and save the electrolyte, refill with water, and "charge" at
about the 40 hr rate for several weeks then replace the original fluid. It is
a long time since I did that [30yrs] it seemed valid BUT I suspect that the
main improvement was due to the draining of the sludge which had previously
been "shorting" the plates at cell bottom. You will have noticed that there 
s
a helluva gap below the plates, before cell bottom.
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