# how to tell if a 12 volt lead acid battery is toast



## degarb

I have several car and mower batteries (12 volt lead acid) that appear to charge completely but are unreliable, often dead. 

What is the symptoms of a bad lead acid battery?


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## jasonck08

Whats the resting voltage of the battery when fully charged? It should read about 12.6v.

Sometimes lead acid batteries that go bad will have a bad cell, and will only read about 10.5 or 11v when fully charged.

Some older LA batteries will perform poorly under heavy discharging. There are testers you can get that will pull quite a bit of amps from the batteries.

If you don't have equipment you might bring it buy an automotive shop like autozone or a battery shop and get it tested.


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## degarb

jasonck08 said:


> Whats the resting voltage of the battery when fully charged? It should read about 12.6v.
> 
> Sometimes lead acid batteries that go bad will have a bad cell, and will only read about 10.5 or 11v when fully charged.
> 
> Some older LA batteries will perform poorly under heavy discharging. There are testers you can get that will pull quite a bit of amps from the batteries.
> 
> If you don't have equipment you might bring it buy an automotive shop like autozone or a battery shop and get it tested.



I wasn't sure the autozone tests were a scam or not.

I have yet to dig out my multimeter from basement. I have three plug in chargers, though, two with just a 10/2 amp charge and one called a battery maintainer with 2 amp maximum and green light auto shut off. All say they are over 100% charged. So, now I know I should be looking for 12.6 volts, I will try the meters. Maybe, I'll try the autozone, if reading >12.6v.


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## Lynx_Arc

the best way is to put a heavy enough load on the battery when it has been "charged" completely. I bought a battery load meter at harbor freight that essentially has a heating element (nichrome wire) that puts about a 100 amp load on the battery and has scales you can see how healthy the battery is. Some batteries will measure properly when fully charged but have weak or bad cells that will basically be unable to supply much current even one bad cell will drop a 12v battery down to 10v under a decent load. I have a few SLA batteries that charge to proper voltage but when I put a ~1.5A load (a two tube fluorescent light) the voltage drops to about 7-8v when a healthy battery should drop perhaps to 11+volts depending on the load/capacity rating. The first sign of a weak battery is the starter gets slower in non cold weather and when cold weather hits you get a surprise of not being able to start the car unless you have fully charged the battery beforehand so that short trips to the store which don't fully charge it up will have you in trouble.


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## Russel

The best way that I have found to check the state of health of a flooded lead acid battery is to check the voltage with a multimeter, charge the battery, check the specific gravity of the electrolite with a hydrometer and perform a load test. 

If the battery voltage (assuming a 12 volt battery) reads less than 10.5 volts and the battery has been sitting like that for a while it's probably a lost cause. It still may be worth charging and further testing if the voltage wasn't drastically low and the battery hasn't been sitting dead for months.

Charge the battery and check it with a hydrometer, usually if the battery is bad (at least in my empirical experience) one or more cells will be drastically different than the others. If that is the case, recycle the battery, it is no longer usefull. If it is only slightly different you might try an equalization charge.

Life Extension Through Charge Equalization ofLead-Acid Batteries PDF file 2.76MB

Then, if the charged battery looks good with the hydrometer, perform a load test. (Or take the battery to get load tested.)

If it passes a load test it should be a usefull battery and should be kept charged.


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## Mr Happy

degarb said:


> I have several car and mower batteries (12 volt lead acid) that appear to charge completely but are unreliable, often dead.
> 
> What is the symptoms of a bad lead acid battery?


You have answered your own question. If it appears to charge completely but then is unreliable, often dead, then it is a bad lead acid battery.

You can't fix them; just take them to the recycling station and buy new ones.

When you have new batteries, remember that the fastest way to damage them is to let them become discharged. You should invest in a good charger and keep them topped up regularly, especially during the winter when they are not being used. Try to avoid leaving any kind of drain on the battery so it goes completely flat (like leaving your lights on in the car). That is the quickest way to destroy a lead acid battery.


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## csa

I agree... if they're not working, they're unreliable! 

Some great tips here for checking the general state though. Thanks everyone!


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## jasonck08

Depending on the condition it IS possible to give lead acid batteries new life. There are kits you can buy for sealed lead acid batteries. Basically you drill a small hole in each cell and put a little bit of some kind of chemical into each cell, then you put in some caps in the holes you drilled to seal the battery. This will only work if the cells are all working at the battery voltage reads ~12v when charged. If you have a dead cell and the voltage only reads about 10.5v or so fully charged then there is no hope.


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## Bones

jasonck08 said:


> Depending on the condition it IS possible to give lead acid batteries new life. There are kits you can buy for sealed lead acid batteries. Basically you drill a small hole in each cell and put a little bit of some kind of chemical into each cell, then you put in some caps in the holes you drilled to seal the battery. This will only work if the cells are all working at the battery voltage reads ~12v when charged. If you have a dead cell and the voltage only reads about 10.5v or so fully charged then there is no hope.



It's my understanding that the chemical is magnesium sulfate, more commonly known as Epsom salts.

Here's an eHow guide detailing the restoration process:

http://www.ehow.com ... restore-dead-car-batteries.html

The only equipment requirement that would involve a significant outlay is a three-phase battery charger. Perhaps someone can chime in on whether it's really necessary, or whether the more common and less expensive trickle-charger will suffice if given enough time.

Please note that I have no personal experience with this procedure...


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## VidPro

As a wee kid Me and a friend sold "X14" magic battery reconditioner.
for some reason which I dont quite understand, the maintance guy at the school buss lot , told me he would buy some, and test it in the old buss batteries, that were in need of replacment.
He got some inital good results, then 6mo or so later tracked us down in class and called us out, Long since forgotten by us by then. and told us that the short term quick fix of the magic X14 battery reconditioner was a total waste, and the batteries he put it in are now finished, as they were to begin with.
I could have known, that the maintance guy knew this stuff was not going to do anything usefull, then for him to actually test it for us, that was sort of special, then to do a followup, when we didn't even care anymore, that was cool.


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## SilverFox

Hello Bones,

Epsom salts will work, but not if you use it the way explained in the article you referenced to.

I read the article twice just to be sure. They are dumping the acid out of the battery and replacing it with Epsom salt water. You need acid to make the battery work.

While a battery charger is necessary, it doesn't need to be three phase.

I have had reasonable success simply mixing up a solution of Epsom salt and water. I figure 1/2 teaspoon of Epsom salt per cell, and just enough water to form a solution. This is added in an equal amount to the cells, and the battery is put on the charger for 24 - 48 hours.

The downside to this method is that the battery only seems to last an additional 12 months, and then it is dead for good. However, I made it through several summers after discovering that my bike battery was dead. I was able to get it functional, enjoy the bike for the summer, then save up to replace the battery the next spring.

Tom


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## VidPro

at the solar cheapskate forum, they will try and find older golf , forklift, and other mega storage batteries (trojan) that others have decomissioned, and attempt to revive them for thier uses.
if they ever achived any usefull results it usually is from electrically trying to achive "desulphation" from various pulse charging method. from hard pulse, pulse overcharging, even high voltage high frequency pulse.
the attempts all seem to be to reassemble plates that are falling to pieces, by trying to electrically shove the metal back onto them :tinfoil: without boiling off.
break up the snot hanging off them, replate the plates. (my words).
dont forget the hydrogen and oxygen comming out, which can explode.

thier levels of sucess from bringing home 450Lbs of toxic Lead waste varies highly , are not what i would call "worth it" but if they ever got anywhere usefull it was that. 
they still end up with a lot of wastefull self discharge. 

none of the methods they use would work with the gelled cells, because gassing into a gelled electrolyte, tried some of them on gells , only made them worse.


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## degarb

SilverFox said:


> Hello Bones,
> 
> Epsom salts will work, but not if you use it the way explained in the article you referenced to.
> 
> I read the article twice just to be sure. They are dumping the acid out of the battery and replacing it with Epsom salt water. You need acid to make the battery work.
> 
> While a battery charger is necessary, it doesn't need to be three phase.
> 
> I have had reasonable success simply mixing up a solution of Epsom salt and water. I figure 1/2 teaspoon of Epsom salt per cell, and just enough water to form a solution. This is added in an equal amount to the cells, and the battery is put on the charger for 24 - 48 hours.
> 
> The downside to this method is that the battery only seems to last an additional 12 months, and then it is dead for good. However, I made it through several summers after discovering that my bike battery was dead. I was able to get it functional, enjoy the bike for the summer, then save up to replace the battery the next spring.
> 
> Tom



You didn't state how the sulfuric acid was replaced. I am assuming a reaction with the epson salt.

The thread brings up two questions: how does a comsumer get a pulse charger, and what is deal with three stage charger. (I have a 1.5 amp maintenance charger and two standard 2-10 amp chargers.)


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## BigusLightus

I've had very positive responses from desulphation. I use it on all of my 12V batts. http://www.pacificbattery.com/batteryminder.htmlThis is what I use. I have two and they are both running 24/7. Seems I can always find a battery that needs some help.


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