Inconsistent Battery --passed test

D

david

Member
Location
mississippi
I'm getting frustrated with the electrical system on my fx. I am alternator and battery number 3. I have a small amp and I thought it was the problem so I unhooked it awhile back, but problem still arise.

The battery seems to hold a charge sometimes. Some days it cranks fine, somedays I have to charge the battery for a little I took it and had it tested-2-3 times. At different places. They say it is good. With my ohmmeter it appears the alternator is still charging. how can I find out what (if) is draining it down? Or should I just replace this battery? I don't want to replace it if it isn't th problem, but I'm not sure how to isolate the issue

Thanks for any tips
 
Start testing your battery every morning before you start the car and logging the results. Also, how exactly did you test the output of your alternator?
 
How i tested alternator The battery with car off 12.4 volts, with car running (alternator) it goes up to 15.5-16.4 volts or so. Checked with a digital ohmmeter
 
You may have a bad cell in the battery so its resistance back to the voltage regulator is bad. There for it keeps telling the alternator that it needs a heavy charge. Your alternator should be putting out around 14.4-14.8, depending on the load. 12.4v on the battery after sitting is a bad battery. It's resting voltage should be no lower than 12.6.
 
david said:
So my alternator is too good? Or the battery is too poor? I'm more confused now
Click to expand...

The voltage regulator manages the relationship between your battery and alternator. Its possible that your alternator and battery are both fine and the voltage regulator is malfunctioning and causing the symptoms you've described.
 
How would I check for that? Would that cause my battery to run down periodically?

---------- Post added at 01:58 PM ---------- Previous post was at 01:58 PM ----------

Where would that regulator be? Doesn't the wire go straight to battery from alt?
 
My car had a bad cell in the factory battery. My symptoms were not starting on the first try every once in a while. Then one day while I was waiting for my brother at a store and had the key on it went dead to start. After researching batteries. I found that there are only 2 that stand above all the rest for Group size 35 which is for our Infiniti's. The best one available is by Bosch... "Bosch Premium Power 35-640B" But you can only get it at Pep boys which aren't in Ohio where I was at the time. So I had to get the next best one which is actually at Walmart which is their "Everstart Maxx-35N (North)" They are both about $90. I've since determined that the Everstart Maxx battery is made by Bosch. So there you go. Just FYI the Duralast Gold 35-DLG and Kirkland Signature 12865 about the same price, are good second choices but they drop in CCA (Cold Cranking Amps) compared to The Bosch and Everstart Maxx. After replacing my battery with the Everstart Maxx my car fires up immeadiately like she used to.

When testing a battery the simple battery check can't always detect a bad cell. With your intermitent problem I'd guess a cell going bad. You'd have to physically look into all the cells to see if one is going bad even then that's not 100% if it's going bad from the bottom. If you have the car apart to take the battery out to check, that's the time to swap it out. (And don't let the walk out mechanic replace it). You have to take the cowl apart to pull the battery out. Do it yourself.
 
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Over charging the battery kills the battery too. So if your voltage regulator is letting 16v to your battery, its killing it.

I don't believe its a bad cell in the battery considering this is his 2nd or 3rd battery with the same issues. He's changed his alt already... All things that lead back to the volt reg being bad.
 
Would buying a optima battery that is designed for higher output alternators/sound systems help my problem? My alt is veer charging my current battery that may be going bad
 
I'm not sure, though many are built in as you've described. You may just have to replace the whole alt... Either way I would definitely not risk ruining another battery (especially a really good one) until you correctly diagnose the problem. There is probably a testing procedure for the alternator/regulator in the service manual.
 
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