RJ> One would hope so.  I wonder how you'd get a charger to determine
 RJ> whether a battery was either severely discharged or had a 
 RJ> shorted cell, though?
 AC> It could be done but I doubt that anyone would take the 
 AC> trouble, given the availablity of qualified service staff. A 
 AC> Smart charger could be designed to evaluate dV/dT ie the time 
 AC> rate of voltage rise and compare this with the terminal volts 
 AC> at that moment.
Shoot,  I guess I'm just going to have to take one of the computers around 
here and couple it to some sort of interface that'll log both the terminal 
voltage and the terminal current,  if I can figure out an easy way to 
accomplish that...   
 RJ> Yeah,  but that's not going to help much with what I've got here.  
ithin
 RJ> this small office at the moment are two group 27 deep cycle batteries, 
 RJ> two 6v/33ah gels,  and four 6v/12ah gels.  No way to test individual
 RJ> cells on those except a hydrometer (one of those is handy too), 
 RJ> but I was thinking more along the lines of some way for a 
 RJ> "smart" charging circuit to be able to tell when it was a lost 
 RJ> cause...
 AC> You have an embarrassment of riches.
No,  I used to work in a battery store...    
 AC> You are doomed to either keep a log of each one and give it 
 AC> tender loving care, or to neglect same in the usual way and buy 
 AC> solutions to the inevitable problems!
This is part of why I've been looking for circuits...
I just "topped off" the two 33AH units,  one was found in storage after I'd 
been looking for it for quite some time and had gone to a terminal voltage of 
3 and change,  the other had just been a while since it'd been charged and 
was showing about 6.2 or so.  I haven't checked out the other ones yet.
FWIW,  what I'm using here is a little dual-output supply that consists of a 
small transformer,  bridge rectifier,  and a couple of caps,  puts out about 
8 and 16,  unloaded,  and pushes those batteries up to maybe an amp or so.
 AC> The resistance of internal busses is significant. Some are of 
 AC> copper clad with lead! Not a well known fact. 
 RJ> That could get interesting if the lead coating were breached,  and may
 RJ> well explain why so many of the failures I saw were "bad connections"
 RJ> where you could see a full charge on all of the cells with a hydrometer
 RJ> but couldn't pull any significant amount of power out of it.  Something
 RJ> inside had gotten to a very high level of internal resistance.
 AC> I have seen an internal [submerged] bridge in a city phone 
 AC> exchange battery, corroded almost right through. The possible 
 AC> effect of an open circuit while passing current [eg on boost 
 AC> charge] bears sober thought!
I've seen the results of that on a couple of occasions,  though it never 
happened to me personally.  I guess that either I've just been extremely 
lucky or my preference for long,  slow charge might have some bearing on 
is.
 AC> The copper or brass inserts were a commercial solution to 
 AC> meeting a severe duty cycle ie maintaining output voltage 
 AC> during overload. Cheaper to use copper than to add more active 
 AC> plates!!
And one way to push those CCA numbers up,  I suppose.
 AC> On that basis, fast charging is bad news and slow charging is 
 AC> good news.

 AC> Me, I just go to K-MArt and buy the largest battery that can be 
 AC> fitted in the engine bay.
 RJ> 
 RJ> So do I,  but mostly because you can get the same CCA rating in many
 RJ> different sized packages,  but a bigger box is going to have more 
eserve
 RJ> power.  What's a litle surprising when you look at those charts long
 RJ> enough is that there are some 4-cylinder motors which require _more_ CCA
 RJ> than the 6 cylinder or V8 engines in the same car in the same year.
 AC> A high CCA rating in a small package is costly and hi tech and 
 AC> I admire the skill of the makers. But a penalty is that the QA 
 AC> needs to be tighter- clearances inside are more critical, 
 AC> separators must perform better etc. I prefer the big 
 AC> conservative designed product.
Same here.  Plus,  you get more reserve power...
 AC> I think some auto makers select a battery without sound 
 AC> technical study. Maybe they get a a good offer from a battery 
 AC> maker and if the application looks carzy, they may get away 
 AC> with it by using the smaller batteries for models ex factory at 
 AC> winters' end!
I notice for one example of this that just about all Chrysler products from 
about the mid-eighties onwards *ALL* take a BCI group 34 battery,  even when 
there's some room for something a little bigger.  The only exception to this 
is the pickup trucks that use Diesel engines.  I've put plenty of group 24 
batteries into vans,  pickup trucks,  etc. where you have the room to do so.
 AC> excessive charging especially of a "full" battery are
 AC> aggressive in removing active material.
 RJ> Sounds like overcharging isn't necessarily a good thing,  then.
 AC> Well, it is still necessary say once annually [equalising
 AC> charge] and is monitored and stopped in time, the injury
 AC> done is very slight. Like putting a heart patient on a
 AC> treadmill and working him hard under supervision. May do him
 AC> the world of good, but there is some wear and tear!!
I wonder what the best regimen will turn out to be for these gels that I have 
here...
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