Charlie Young wrote in a message to Roy J. Tellason:
> I've acquired, recently, about a dozen or so gel batteries...
> I'm told that the reason they were being disposed of is that
> they sat on the shelf for too long.  With only one exception,
> they seem to be showing me good voltage,  though.
> The part that bothers me about it is the idea of connecting all of these in
> parallel,  I keep thinking that there ought to be a better way.
 CY> I have been able to get some lead acid gel cells going that had 
 CY> never been used and sat on a shelf for over 5 years. 
These weren't that bad,  the worst one showed me a voltage of around 10 and 
some change...
They also weren't that old,  several of them having dates of 1994 on them.
 CY> The open circuit voltage was low, and under load there was no 
 CY> voltage.  
I haven't tried loading these with anything (yet).
 CY> Hooking the battery to a conventional charger showed no current 
 CY> flow.
I'm getting current flow with a little "power supply" hooked up to 'em.
 CY> Connecting a lifeless battery in parallel with good batteries 
 CY> for charging will result in the good batteries being charged, 
 CY> and the lifeless battery just hanging around not taking any 
 CY> current. 
I hadn't considered doing that,  but more the idea of hooking these in 
parallel with each other.  I'd rather come up with an arrangment that 
provides for some isolation,  if possible,  both in the charging end of 
things and on the load side,  if I can figure out a way to do so without 
introducing too much of a drop in the circuit,  particularly on the load 
de.
 CY> The solution that often works is to use a constant current 
 CY> charger.  I use the same home brew charger for 2V and 12V 
 CY> batteries.  I set the current to C/20 or C/40 and let it charge 
 CY> for a couple of days.
Do you have a circuit for this?
 CY> At first there will be almost no current flow and the voltage 
 CY> across the lifeless battery may be 3 to 30 times the rated 
 CY> voltage.
I've been seeing current flow with these all the way along.  The bigger units 
drew a bit more at first but settled down quickly,  while the smaller ones 
seem to be taking longer to do the same.  I took the bigger ones off when the 
current had gone down below a quarter of an amp or so,  just as a convenient 
cutoff point so I could get to them all eventually.  This smaller one that's 
on charge now is still showing me a current of just under 400 mA,  and has 
been in that general range for several days.
 CY> I can hear the controversy coming now :)  This does not cause 
 CY> the battery to explode -- at C/40 it doesn't even get warm to 
 CY> the touch. Only too much current will cause problems -- not too 
 CY> much voltage. The constant current charger lowers the voltage 
 CY> when the battery starts taking a charge so that the current 
 CY> remains at a safe level that will not damage the battery.
These being 10 AH units,  a current of 400 mA is what,  C/25?
 CY> After the first day the voltage across the battery should be 
 CY> slightly above the rated voltage of the battery and the current 
 CY> should be up to whatever you set as the limit. 
I think that the limit in this case is being set by the little "power supply" 
(transformer-bridge-filter) that I'm using,  it seems to be capable of maybe 
a bit more than an amp or so of output.
 CY> Another day or two of charging and the battery will be up to 
 CY> its full potential.  At C/40 you can charge the battery for a 
 CY> week or two and not hurt it.
Some of these seem to be headed in that direction,  as far as duration is 
concerned.
 CY> If the voltage goes below the rated battery voltage while 
 CY> charging, you probably have a shorted cell and should discard 
 CY> the battery.
At what point is it safe to assume this?  I'd like to automate detecting this 
condition if it's at all possible...
 CY> Depending on the maximum voltage your charger will supply,
 CY> you can connect several batteries in series.  Examples;
 CY> Let's assume;
 CY> - your charger can supply 48V
 CY> - you are trying to rejuvenate lifeless 12V 10 AH batteries
 CY> - you choose to charge at a rate of C/30
 CY> You can connect 1 or 2 batteries in series and set the
 CY> current limit to .33 amps.
 CY> You could charge 3 normal batteries at once using such a 
 CY> system. This system can also be used to charge Nicads. Actually 
 CY> the right way to charge Nicads is to use a constant current.
 CY> These restored batteries may not have the same amp hours as 
 CY> they did when they were new, but they should have many charge / 
 CY> discharge cycles left in them.
Oh yeah,  I don't expect these to act like the newer ones would,  but I do 
expect to get some use out of them!
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