[s-cars] dead battery

[Brett Dikeman]

 >Anyone else enjoying multiple battery deaths in the wonderful heat  
this summer, Houston in may case?
 > Went out yesterday morning to start the RS2'ed S6 after it had  
been sitting under cover in the garage for about 2 1/2 weeks...dead  
as a doornail.
 >Internal battery short???

Lead acid batteries self-discharge and sulfate very quickly in heat.   
2x the rate at 95 degrees vs 70 degrees.

See below on shorted cells.

 > It was fully charged and fine when last run.

Fully charged how?  Put on a multi-stage charger?  Or just started up  
and run for a bit?

   Alternators don't do a very good job of properly charging  
batteries, especially dead ones; a 90A alternator, for example, that  
only has 30A 'free', will take over two hours of moderate engine  
speed to charge a battery fully (charge time is > Ahr capacity /  
charge rate in Amps, it's not a 100% efficient process).

 >Went to charge up my spare, sitting not far from the front of the  
car next to a large stack of bricks, and it seems dead, too

What was the voltage and specific gravity?  Appearance of the plates 
(color/texture) and electrolyte level?  Watch out for a shorted cell  
(one cell that looks different from the others, and a battery that  
starting gassing before 13V while charging.)

 >  It was last charged up ten months ago, four months past the usual  
duty for me.

Recommended storage period (not on a float charger) for most lead- 
acid plate batteries is about 2 months tops in cool (less than 60  
degree) temperatures.  It drops to a month or less in heat.

Buy a maintenance unit, like a battery tender, for storage.  Yuasa  
among others OEMs from the same company Battery Tender uses to make  
their chargers.  DO NOT get a 'trickle charger'.  The Yuasa I have  
every few weeks will stop float-charging and do a complete charge  
cycle, then go back on float; the wall-wart units are about half an  
amp, and the unit i have is 1.5A.  I think they make 10A units, but  
they're pretty pricey.  Read the manual- if it says "do not leave  
connected", return it.  If it states that it comes on every so often  
to re-charge the battery but doesn't mention a float stage- return  
it.  Good signs are things like microprocessor controlled multi-stage  
charging, and talk about float voltages (float should be temperature  
compensated, but many chargers don't do this, so try to store the  
battery around room temperature).

FYI- NEVER charge a dead battery at high rate; this is a sure fire  
way to kill it.  Yes, it'll take a day or more, but lead acid  
batteries don't like being discharged very slowly and charged fast.   
Particularly on a poorly built or older battery, if you gas the  
battery too much, plate material can flake off and short out the  
cell, which is pretty much permanent death(unless you feel like  
emptying the electrolyte out somehow, flushing out all the toxic  
lead, refilling with fresh electrolyte, etc.  Yeah, I didn't think  
so.)  At the very least, bring it up to about 12V slowly, then charge  
it at a faster rate.  Keep in mind that the C/20 max charge rate  
applies to a fresh battery; if your battery has been sitting a while,  
the plates could be sulfated, reducing capacity.  This is what  
actually kills a lot of batteries- they get charged too fast for  
their sulfated condition. Something else to watch out for in the  
wintertime- the freezing point of the electrolyte in a battery RISES  
SIGNIFICANTLY as state-of-charge drops.  A dead battery in the  
wintertime could EASILY be FROZEN.  Charging a frozen battery is a  
good way to blow one up.

Vector makes a charger that has a desulfate feature.  Although I'm  
not convinced it actually does much, I haven't done any good tests to  
"prove" things one way or the other.  There are various kits and  
widgets available for purchase (some at outrageous prices for what is  
little more than an inductor and 555 timer).  They usually work by  
sending an extremely short high voltage/high current spike to the  
battery to cause the sulfide crystals on the plates to go back into  
solution.  If you google "desulfator", you'll find some links to  
homebrew units which are widely reported to work (if slowly; days or  
weeks).  Success is measured by how well the battery clamps the  
spike, basically- a sulfated battery won't, and a good battery will.

The Vector tends to be pretty fussy about whether it'll actually  
charge a battery.  Mark Chang left his S4 parked WITH a solar charger  
per my recommendation; came back a month+ later, battery was dead  
(we're not sure why- he swears he triple-checked interior lights and  
such.  I think it may be the aftermarket stereo gear).  I took it  
home and charged it for him- still charging actually- and it was at  
about 6V.  Beyond "discharged", ugh.  Even after bringing it up to  
almost 12V, the Vector displayed "F03", sulfated or shorted cell.   
Except the battery seems fine, just discharged.  My Yuasa (1.5A,  
uuuugh, slow) is taking forever to charge it, but doing so without  
"complaint".  I also don't really recommend it because the clamps are  
VERY stiff(digs into the soft lead of the posts) and they're huge-  
making it very hard to get the clamps onto many terminals, including  
the jumper posts in C3/C4/V8q's.

One of the reasons you've had better luck with Optimas is because  
they're basically AGM batteries with different cell construction; AGM  
batteries self-discharge much slower than standard car batteries.  I  
believe they can be stored at least 6 months with no harm; I think I  
might have read Optima says they'll do a year without too much  
discharge.

Storage does NOT mean "connected to the car"- the car will drain the  
battery at a rate anywhere from 25-100+mA.  At the very least,  
disconnect the + terminal if you're going to be gone more than a week  
or two.  Remember- the cooler the battery, the longer it will last.   
In the basement on cool concrete is perfect (no, plastic-case  
batteries won't discharge sitting on concrete, even if they're wet).   
One other tip- wash any electrolyte off the case of the battery,  
particularly the top, before storage; enough electrolyte will conduct  
electricity across the case and speed discharging.  Warm water and  
baking soda will do nicely.

Taken car of properly, lead acid batteries will last quite a long  
time.  Also- please make absolutely sure your battery gets recycled,  
not thrown away (like ALL types of batteries!  Especially  
rechargeable batteries of ALL types, they contain heavy metals, as do  
many electronics, that have ZERO business being in a landfill.  Ie  
DON'T toss that old broken cell phone in the trash!)

More info than you ever wanted to know about lead acid batteries:
http://www.uuhome.de/william.darden/

I'd recommend the solar panel widgets, but not until Mark and I  
figure out why the one he bought failed miserably.

HTH,
Brett
-- 
"They that give up essential liberty to obtain temporary
safety deserve neither liberty nor safety." - Ben Franklin
http://www.users.cloud9.net/~brett/