Normal Battery Voltage
 

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.

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.

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.

My Voltage is 13.5-13.7 when running

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!

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.

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.

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?

Ah, west coast...

Yeah, it is a quick process. They connect the tester to the battery jump contacts under the hood while the engine is running. That is pretty much it. They can switch back and forth between your battery and alternator to see what is going on.

Nice. Free information, such a deal!

Just a word of advice if you need either a battery or alternator, I would feel absolutely fine buying a Duralast battery from them, but I would not buy a remanufactured alternator from them if that ends up being your issue.

Thanks for that. I have an Interstate that has a month left on the replacement warranty. If it is the battery, I'll be going back to them to try to get it replaced. If it is the alternator, I was thinking that this would work:

Your Parts Search Returned 1 Part(s)

Do you have any other recommendations for alternators? Unfortunately, it seems as if the place that did the $200 rebuilding mentioned in a DIY here is no more...

The link you provided looked pretty good. It's Bosch.

You can also look here;

www.bavauto.com

Pelican Parts - Porsche Parts & BMW Parts - Automotive Parts and Accessories - Porsche & BMW

If you are in a pinch and can't wait for shipping, you may be able to find a Bosch unit at a local Napa Auto Parts. I would think it would be cheaper than dealer, but you never know.

After getting a jump start at work, I made my way to Autozone where they tested the battery and got a "Charge and Retest" message. They offered to charge it for me, but said I had to pull it and bring it inside. At 8 PM, I didn't feel like that was an option. I don't think they realized what was involved.

I picked up a load tester and tested the battery when I got home. It tested good at rest and marginal under load. The charging system tested OK.

I left it on the BMW cigarette lighter trickle charger overnight and locked it. I had 12.2V this morning and it started easily.

I'm going to bring it to the place where I purchased the battery for testing since they can replace it under warranty if it fails testing.

Plan for this weekend is to remove remaining third party electronics (except the Dension Ice Link) and perhaps fuse 74 if I can live without it (not sure if I'll be able to sync Bluetooth and use handsfree without 74).

Battery and charging system passed testing. The battery tested "GOOD - RECHARGE" at 12.28V and 744 CCA (rated 850 CCA). I plan to start the hunt for battery drains.

Yikes, I was hoping it was just going to be your battery or something else easier to diagnose than a drain. Good luck on the search. Isn't the final stage resistor a common drain issue?

Thanks for positive thoughts. You're right about the FSR, but I replaced it a couple years ago. Now on to reviewing the testing procedures for detecting battery drain.

I am having the same problem, battery goes dead whenever volts at 13.4 when running on dash. Have you figured yours out yet.

For the E53 X5 during Quality Certification I the display vehicle check that is carried out by the technician calls to maintain battery voltage at 12.65V minimum. Interestingly for the E70 X5 beginning 2007 this specification changed to 12.3V minimum.

My 2004 4.4i routinely is reading 13.5-14v (monitoring through the unlocked test functions on the OBC). But I've had several occurences (in a several month period) where it only reads 10v or so. If I stop and restart, it goes back to normal charging. Alternator on its way out perhaps?

Any have any thoughts on this voltage problem? Thanks!