Normal Battery Voltage

scchang · #1 03-14-2010, 01:31 PM

I've searched around here but can't find the answer to this, so please don't flame me for asking: What are the normal voltage values for the battery when testing from the OBC?

I get 11.4 and 13.3 when running. When I rev the engine or turn on various electronics, the 13.3 does not really change.

The issue I am having is in a 2001 4.4i with 158,000 miles. The battery is less than a year old but has been discharged to requiring a jump twice. The alternator is original. I had some aftermarket electronics that have since been disconnected, but continue to experience the battery drain. It usually occurs after the vehicle hasn't been driven for a couple days or more. I've read the various posts regarding pulling fuses, etc. but thought that if my voltages indicate a bad battery or alternator, I could address them first.

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JCL · #2 03-14-2010, 01:45 PM

I would expect 12.5-12.8 volts for the battery itself, and in the upper 13 range with it charging. Not sure what the official BMW figure is.

Your battery could just be low, and your alternator could be the problem.

Penguin · #3 03-14-2010, 11:43 PM

I am not familiar with the E53 charging system, but I would expect to usually see 13.8 volts when the engine is running on most vehicles.

My E70 runs about 14.3-14.8 volts when the engine is running, but the E70 uses an AGM battery as OE, and they typically like a higher voltage, e.g., a couple of tenths or more, as compared to the older flooded-cell batteries.

bgsquad · #4 03-15-2010, 03:46 AM

My Voltage is 13.5-13.7 when running

FSETH · #5 03-15-2010, 11:06 AM

Quote:

Originally Posted by scchang

I've searched around here but can't find the answer to this, so please don't flame me for asking: What are the normal voltage values for the battery when testing from the OBC?

I get 11.4 and 13.3 when running. When I rev the engine or turn on various electronics, the 13.3 does not really change.

The issue I am having is in a 2001 4.4i with 158,000 miles. The battery is less than a year old but has been discharged to requiring a jump twice. The alternator is original. I had some aftermarket electronics that have since been disconnected, but continue to experience the battery drain. It usually occurs after the vehicle hasn't been driven for a couple days or more. I've read the various posts regarding pulling fuses, etc. but thought that if my voltages indicate a bad battery or alternator, I could address them first.

Do the numbers fluctuate when you are testing at idle? If they are changing more than half a number or so, you are more than likely having an issue with your voltage regulator/alternator.

scchang · #6 03-15-2010, 12:53 PM

Quote:

Originally Posted by FSETH

Do the numbers fluctuate when you are testing at idle? If they are changing more than half a number or so, you are more than likely having an issue with your voltage regulator/alternator.

Good question. There is a little fluctuation, no more than 0.2V though. While driving, I'm seeing 13.4-13.6V.

What I don't understand is how it could start after sitting for a couple days, be driven 12 miles, sit for five hours and then not start.

Then, after being jumped, driven home another 12 miles, sit for a couple days and start again.

It doesn't make sense that this little bit of driving would adequately charge the battery, but what do I know!

FSETH · #7 03-15-2010, 01:06 PM

Quote:

Originally Posted by scchang

Good question. There is a little fluctuation, no more than 0.2V though. While driving, I'm seeing 13.4-13.6V.

What I don't understand is how it could start after sitting for a couple days, be driven 12 miles, sit for five hours and then not start.

Then, after being jumped, driven home another 12 miles, sit for a couple days and start again.

It doesn't make sense that this little bit of driving would adequately charge the battery, but what do I know!

The alternator on my e36 fried out, I replaced with a remanufactured unit and noticed that my lights (interior/exterior) were pulsing a little. Went down to Autozone and had them test the alternator and they found it was fluctuating about 0.50 - 1.0. Ended up being the voltage regulator.
I put in another remanufactured alternator and all is well.

I just replaced the battery in our X a few weeks ago. One morning (after sitting all night) it started up fine. Then my wife shut the car off at a gas station about 2 miles down the road and the car would not crank. I was a little surprised it started normal just a few minutes earlier then would not start at all in such a short period of time. There really wasn't much of a warning that the battery was loosing charge.

scchang · #8 03-15-2010, 03:16 PM

I'm Autozone-bound this afternoon...

FSETH · #9 03-15-2010, 06:41 PM

Quote:

Originally Posted by scchang

I'm Autozone-bound this afternoon...

Well, did you find out anything? They will test your battery and alternator on the spot with a small hand held load tester. It only takes a few minutes as you may already know.

scchang · #10 03-15-2010, 06:52 PM

Quote:

Originally Posted by FSETH

Well, did you find out anything? They will test your battery and alternator on the spot with a small hand held load tester. It only takes a few minutes as you may already know.

I'm on Pacific time, still at work. I'm going as soon as I get through and will post back. Good to know that it is a quick process! Do they access the battery directly, use the under-hood terminals or do something else?

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