battery charging and death

[Brett Dikeman]

Ed Kellock wrote:

>My Coupe GT had a new battery last July.  Over the last couple months the car has sat unused for longer periods of time.  It required a jump and then would be okay until it sat again for several days.  This is generally not a common problem for the car.
>  
>
Charging by alternator (or worse, those charger-on-wheels you see at 
repair shops) is unfortunately not very good for a dead battery.  Charge 
profile is supposed to match discharge profile, and you should never 
charge a battery over its max charge rate(generally C/20).  Charging by 
driving  also rarely results in a good, full charge as people don't 
realize how little juice actually is left over in most cars to charge 
the battery- and alternators don't multi-stage charge.  Intelligent 
maintenance chargers with a few amps are best for this.

>According to Mike LaRosa and "Tony & Lillie", 12.8 is the baseline heathly battery charge.
>
Depends on temperature.

>  After charging mine to about 13.03 on a 2-amp charge, it settles to about 12.3 when the charge is removed and then slowly starts to trickle down, the last reading was 11.85.  So I'm think it's dead, Jim.
>  
>
Possible.  How dead was the battery when you put it on charge, and how 
long did you charge it?  Fully discharged to very low voltages, it can 
take a day or two at 2Ahr, since car batteries are well over 40 A/hr, 
and capacity is from full charge voltage to manufacturer's recommended 
minimum voltage, not anywhere near under 11 volts.  Also, charging isn't 
a 1:1 relationship; 2 hours at 2A/hr does not put 4 A/hr into the battery.

>So did I kill it?
>
Sounds either undercharged or has a shorted cell.  If it gases while 
charging at 2Ah/hr and such a low voltage (gassing shouldn't start until 
almost 14v), you probably have a shorted cell.  It will be obvious if 
you take off the caps- one cell's plates will be different than all the 
others, because it will have sulfated(because that cell was discharged 
to zero volts).

  As a whole, sulfation reduces battery capacity, not voltage.  If the 
entire battery was sulfated, voltage would skyrocket with charging, and 
would appear normal just sitting there until you went to draw current 
from it.  My charger applies a slight charge (maybe 100mA) and watches 
voltage- if it rises too much for what is a minimal amount of juice, it 
shuts off, diagnosing the battery as sulfated.  On a sulfated battery, 
i've seen that 100mA or so cause the battery to hit 16V within a few 
minutes.

Because it reduces battery capacity, sulfation can cause other problems- 
gassing from overcharging, which leads to boiloff as well as shorted 
cells from charging too fast (the gassing, if it gets violent, tears 
apart the grid, and the pieces of the grid fall to the bottom of the 
cell, pile up, and short it out).

Some gassing is good, especially for stationary batteries; the bubbles 
stir up the solution and even out the specific gravity across the height 
of the cell.

>  I was going to use the KnowledgeBase item to check for a drain on it, but I figure that's moot until I get a battery that will hold a charge first.  
>
>Do peiods of inactivity kill a battery?
>
No- anything less than full voltage causes sulfation, more so in warm 
temperatures (sulfate and self-discharge more rapidly) and more so as 
voltages drop.  Batteries in long term storage should be kept in a cool, 
dry area and either topped off every month(both in terms of charge AND 
distilled water) or kept on a regulated maintenance charger (NOT a 
trickle charger) and checked periodically for proper electrolyte 
levels.  Clean the top thoroughly of any traces of electrolyte before 
storing it.  Storing modern batteries with plastic cases is OK on 
concrete or any other surface (used to be old batteries would discharge 
from condensation that built up between the case and a cold floor).

>  Or just an already compromised battery? 
>
Could be.

> Would a constant slow drain kill it?
>
Yes, but lead acid batteries self-discharge, faster at higher 
temperatures.  Maximum storage for a disconnected standard lead acid 
battery is ~1 month at 60 degrees or so, tops.  VLRA's(modern 
"gel-cells") can be stored longer.  Optima claims up to a full year, I 
believe, because of capacity, cell construction and the chemistry.

>  Did I just get a bad battery from the get-go?
>
>  
>
Quite possible.  Always check manufacture dates if possible and buy from 
a location which does lots of business.  Ask they fully charge and test 
the battery; look at the results before you accept it.  A really, really 
good battery dealer will keep stock on a maintenance charger system.

One or two companies OEM the majority of lead acid maintenance 
chargers.  Battery Tender, Yuasa, and others sell wall warts for 
ATV's/motorcycles/lawn stuff, mid-sizers in the 1.5-2A range for larger 
stuff like boats and cars.  Battery Tender also makes a much larger 
charger(10+ amps) but it's $$$.  I ended up with a 1.5A Yuasa unit, 
because that's what the local motorcycle shop could order for me, and 
shipping etc was free if I was willing to wait 2-3 days.

If you want to learn everything you ever wanted to know about lead acid 
batteries (and check what I've said), google for "lead acid battery FAQ" 
(use quotes).  There is an excellent document written by a guy named(I 
think) William Darden (or something similar).

If the battery is sulfated, be forewarned desulfating them is a very 
long process...days or weeks are involved.

The solar units...anything under 100mA will not be enough to counter 
both accessory drain(clock, ECU, radio, etc) and the battery's own 
self-discharge, especially in northern areas, and they're a great idea 
for a vehicle which is used infrequently (not for storage though- that's 
best left to a maintenance charger).

Brett

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