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Wierd battery problem - BATTERY THEORY NEEDED

Can Can

Can Can

Pusher Man
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Cochrane, Alberta, Canada
I'm almost positive my battery is shot. I can charge the sucker up and it will start the truck no problem but after a couple of days it needs a charge again.

The wierd part is that my DMM is telling me that the battery isn't dropping below about 11 volts. I checked it again today and it read 11.6 but wouldn't start the motor. I hooked up the trickle charger and after 5 minutes I turned the key just for shits and giggles -there was enough juice in the battery to get the motor started??????

/forums/images/graemlins/thinking.gif /forums/images/graemlins/dunno.gif /forums/images/graemlins/dunno.gif /forums/images/graemlins/dunno.gif

How can 5 minutes on a trickle charger give the battery enough power to turn over the motor? And how come the sucker isn't dropping below 11 volts? And why on earth isn't 11 volts enough to start the motor in the first place?

FWIW, I'm gonna swap in a new battery. I'm just curious about the theory behind this wierd situation.....
 
from what I have heard about batteries is that a battery with 12.0 volts is considered dead. My Optima is usually around 13 volts.

I am not sure 11 volts will start a motor. What kind of battery?

Harley
 
Well, that kind of explains things, eh? /forums/images/graemlins/doah.gif

I never knew that anything below 12 volts was considered a weak or dead battery. I just assumed that 11.5 would be plenty....

Any idea why 5 minutes on the charger would be enough to turn the motor over?
 
5 min would be enought to "shock" the batt, providing you with just enought to start it but ya a 12 volt system usually runs at about 13.5 volts
 
Well, actually, its not the voltage reading that makes a battery unserviceable. Its the capacity. When you have a battery sitting not hooked to anything, it may read 12v, but as soon as it gets a load on it, even as small as a 100W KC light, it wont run it because the battery cant supply the voltage. If you had a multimeter on the battery when you hook the light up, you would see the voltage reading drop right to like 8 or 9 (just for an example). Thats why, when you take a battery in to a shop to get it tested, they not only read the voltage static (no load), but they hook it to a load tester and drag it down as if it was cranking a starter, then read it again. A good battery should be able to supply a decent voltage for a certain length of time based on the CCA (cold crank amps) and A/H (amp/ hour) rating of the battery. If it cant, the battery is possibly shorted inside, or enough of the plates are deteriorated from bad water etc. Its best to use distilled water in batterys, because tap water has so many contaminants in it that the plates corrode and fall apart a lot sooner. Also, Ive found that the deep discharge type batterys (like Optimas or some Marine brands) woill last longer on vehicles with winches because the batterys get drawn so hard, then charged and drawn again that it just plain wears them out.

Id take the battery in to get it tested... the reason the charger may help start it may be the battery, but it could also be a bad contact somewhere... a high resistance connection that only requires a little extra umph to get things cranking.
Most shops will test batterys for free... if they think they can sell you a new one! /forums/images/graemlins/smile.gif

Good Luck Paul!

Mike
 
Sounds like the battery's internal plates might be "sulfated". A layer of sulphur compounds builds up on the lead plates and keeps the electrolytic reaction from going on. There's a few chargers on the market that advertise being able to reverse the sulfation. Either Four Wheeler or 4W&OR did a review on one recently (I think...) and they had great success reviving a "dead" battery. Might want to check it out...

When I get home from work, I'll look through my stack o' mags and see if I can't find the article in question.
 
13.5-14V is considered normal for a running engine. With the engine off, a good battery should be 12-13V without a load. Cranking the engine, it could drop down to 9 or 10. This is not a problem, as every battery has internal resistance. Resistance x current = voltage drop.
 
Yup, eight years old, Harry. A new one is on order.

[ QUOTE ]
FWIW, I'm gonna swap in a new battery. I'm just curious about the theory behind this wierd situation.....

[/ QUOTE ]

/forums/images/graemlins/deal.gif /forums/images/graemlins/wink.gif
 
8 years old, and you think you need a new battery? /forums/images/graemlins/dunno.gif You Canucks kill me /forums/images/graemlins/whistling.gif /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif

John
 
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