Battery Voltage...

afast93stang

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#1

• Dec 4, 2006

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So I bought an Optima battery, in October and I was waiting until I got an aluminum battery tray. I installed the Optima battery and it didn’t have enough of a charge to start the car.

I then took it down to Oreilly's and they charged it for me, I get home it worked fine, drove it around for a while and put it back in the garage. This morning I come out and it won’t start. I jump it and it fires right up, drive around a little and go back home and I turn it off and try and start it back up again just to see. It doesn’t start...

I get out my voltmeter and it reads at 10.12 and about every two to four seconds the numbers keep dropping... My Ford shop manual says it should be at 12.4 volts, do I have a bad battery that keeps discharging on its own or what?

 

jrichker

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#2

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The battery charge should read 13.8-14.2 with a warm engine and a properly working alternator. Most auto parts stores will check your charging system for free.

A battery that charges up and then goes flat overnight usually has something draining it while the engine isn't running.

Typically it is something draining the battery. Small things like glove box or courtesy lights are often the culprits. If you have an aftermarket stereo or alarm system, it is also suspect.

The ideal method is to disconnect the positive terminal, and connect a Digital Multimeter (DVM) between the positive terminal on the battery and the positive cable. Set the DVM on a low current scale of 2-5 amps if it doesn't auto range. Watch the current draw, and then start pulling out fuses. When you see a sudden drop in the current, that circuit is the likely culprit. Note that the computer, radio & clock will draw less than 1/10 amp to keep the settings alive.

See http://assets.fluke.com/appnotes/automotive/beatbook.pdf. You will need the Adobe Acrobat viewer which is also a free download – http://www.adobe.com/products/acrobat/readstep2.html

 

afast93stang

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#3

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The battery wasnt hooked up overnight, I made sure to disconnect the wires because I left the hood open because I later changed out the starter relay.

Also the battery was dead when I put it in the car originally. Its build date sticker says 6-06. It shouldnt go that dead so quickly should it?

 

afast93stang

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#4

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I just did the fuse thing, and there wasnt any change in the voltage draw. Whats next?

 

bullitstang1313

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Dec 4, 2006

#5

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Take the battery to an autoparts store and let them load test it. If you just bought it, you should be able to take it back and get a new one.

 

P

postalbunny

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#6

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You got it uncharged as well too right? Sounds like you got a dead battery. I would say check the water level, but I think those batteries are the sealed kind. You could try letting the shop charge it up again, and let it sit overnight not hooked up to anything and read the voltage.

It's possible your alternator isn't charging your battery and you're draining it that way... i'd check voltage /w the car running, should be above 13vdc.

 

afast93stang

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#7

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I just spoke with my families mechanic, he was saying when Orielly's charged it, they put a surface charge on it. He said what I need to do is use an 10v overnight chrage on it to give it a complete charge. Any thoughts?

 

bullitstang1313

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#8

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If it still died after driving around on it then it could be a dead battery. You should let Oreilly charge the battery and then load test it. This will tell them if the battery is truly bad or if it didn't get charged enough. Voltage should be 12.4 to 13.2 volts while the engine is off. With the engine running you should see voltages around 14.5 or so depending on what accessories you have on. Your charging system could also have been the culprit. If the alternator wasn't working then the battery would have been taking all of the load. If the battery is truly dead you should be able to have it replaced no charge since it is less than a year old.

 

HISSIN50

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#9

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Too many variables. You have the tools from this thread to get it whipped though.

Your mechanic meant to charge it with a 10 amp charger (not 10 volt).

If the car started with this battery but then went downhill, I'm not so sure I'd immediately blame the battery. I'd revisit JR's post about ensuring that the alternator is charging and that the charge is reaching the battery (compare voltage at the alt's charge stud vs voltage at the battery). The numbers JR posted are for a car that's idling. If you're seeing voltage in the 12's with the car idling, the charging system is suspect.

Good luck.

 

afast93stang

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#10

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Like I said the car only started with this battery when jumped, it was dead or low when i bought it.

After I had it charged by Oriellys on Sunday, it sat overnight and was disconnected and still wouldnt start up this morning.

I have checked the things that JR posted, thank you for the quick responses and help btw.

My charging system is a 130amp PA Performance that is a year old and it puts out 14.4 volts when running when I jump started and tested it this morning.

I went ahead and bought a 10amp charger. The battery was reading 50% power when I hooked it up to charge it...

 

HISSIN50

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#11

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Sorry - I guess I thought it started on its own after the parts store charged it up.

I might guess when you mentioned that it's reading 50% power (I don't have a newer battery charger so maybe they do actually tell you some percentage reading) that means the charger is reading 5 amps right now. If so, it's thirsty.

If the battery never started the car on its own and it acts up again after you charge it yourself, then I'd consider swapping the battery.

Good luck.

 

afast93stang

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#12

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So the charger I picked up says it will charge a battery in 3 to 5 hours. I went to class and ate dinner so it was a good 5 hours that it charged for. When I got back home and checked it the reading on the display said it was fully charged.

I take a reading on the battery before I start it and it reads 12.xx with my multimeter.

I try and start the car and it half cranks once then dies. I test the battery with my multimeter and its reading back down at 10.xx volts. I hook the charger back up and it reads 0 charge on it.

Is it safe to say I have a bad battery now?

 

onefstsnake

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#13

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Did the car do this with the last battery you had?

if it was fine before the optima id say its a bad battery. But I did have a 130A PA alternator die on me in less than a month (bad diode) But it seems like yours is fine.

Id get the battery load tested. You want a charger that charges overnight at a low Amp rating.

Or just call Optima and see what they wanna do.

 

afast93stang

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#14

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This charger has a 2amp setting, should I try that overnight?

No the car didnt do this with the other battery.

 

onefstsnake

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#15

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well 95% its a bad battery.

I would put it on the lowest rating and let it go.

should take 15+ hours. But I would call Optima first.

 

afast93stang

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Dec 5, 2006

#16

• Dec 5, 2006

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The vertict, it was a bad battery from the start.

I take it back to the place I bought it and the first guy who I talk to says he has been selling Optima for 15 years and he has NEVER seen a bad one...

Im thinking great, I dont want to deal with him... thank god he was busy and someone else helped me. I got a brand new battery and the stang fired up on the first try.

 

HISSIN50

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#17

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