Battery Voltage

I recall a thread a few weeks ago the battery voltage at idle & under load. I tried searching for it & can not seem to find it.

I suspecting I may have a battery that is close to needing replacement. Looking at the OBD Test 9, at idle the voltage is about 12.5-13.4, at a full stop voltage is 12.0-13.4, while driving the voltage is 13.8-13.9.
All this was with the radio on, brake lights & turn signals under city driving stop & go situation. With the head lights on, voltage was about the same as above.

It's an aftermarket battery. I'm not sure of its age as it came w/ the car. I've tried looking at it to try to find any dates but nothing. All connections are tight. Alternator seems to be functioning correctly. Any ideas, suggestions or thoughts?
Cheers,
Larry

I'm pretty sure OBD #9 is for alternator voltage not battery voltage so you can have 13.8V on OBD but a dead battery.

There's a chart somewhere about measuring with a voltmeter at the battery after surface charge is removed by turning on headlights for a minute than reading voltage across + and -.

Bluebee has a copy or simply search for e39 battery on the forum.

Iirc there was a chart that Q posted with normal voltage thresholds listed. I was trying to find that particular thread to help diagnose if what I was reading was normal or below tolerances. Ill try to do another search when I get back to a computer vs my blackberry.
Cheers,
Larry

Is this the one?

OBC TEST 9 shows battery voltage when the ignition is in position 1 or 2 (engine NOT running). The best check is with the ignition in position 1 since that position has the fewest electronics turned on or running. In ignition position 2...all of the car's electrical components are running or "primed" so-to-speak.

If the engine is running...then you are looking at the output of the alternator/charging system. And if you also need to check the battery's voltage either before starting the car or approx 2 hours after shutting down so that you aren't looking at the "surface" charge of the battery just being replenished by the alternator.

Are you looking for the "battery state of charge" chart? If so, here it is below: (again, ignition should be in position 1 with the engine NOT running)

I don't like that voltage. Something is amiss with your electrical system. Under full load, my car still is >13V.

The test just what the vehicle circuits are running at. It is supposed to he buffered by the battery so under full load at idle like above the battery will drain to keep supplying power when the alternator can't keep up. This doesn't seem to be happening on your car. I'm not sure what the significance of that is.

There you go, Q, right on cue.

thanks everyone for the help. i will be looking at this more tommorrow. hopefully, i will be able to find something definative after testing.
cheers,
larry

As soon as I buy a voltmeter, this info will be very useful. Thanks.

Originally Posted by dvsgene

There you go, Q, right on cue.

I'm gonna add that one to the best quotes!

Originally Posted by Edgy36-39

As soon as I buy a voltmeter, this info will be very useful.

This thread has all known battery-testing details, much of it, on cue from Saint Q himself:
- DIY how to test a BMW E39 battery & alternator

Note: If there are additional battery-test procedures, please let us know so we can add them.

this morning after letting the car sit overnight for 8+ hrs, obd voltage was reported at 11.5 w/ the key in position 1 & car in park. after starting, voltage dropped to 9.2 & slowly increased to 13.8 at 800 rpm. on the drive in this morning w/ headlights on, the voltage was not as drastic as reported yesterday. remained steady at 13.0 when braking -> 13.8 at full stop. idle was at 13.4-13.9. driving was reported at 13.8-13.9.

i will be running the load tests this afternoon after work since doing this at 5am in the dark was not too feasible. thanks again everyone for all the suggestions & help. i will report back my findings.
cheers,
larry

Originally Posted by Monkeyking

i will be running the load tests this afternoon after work

I've spent about 15 hours updating the procedures for checking the battery (and ran them myself) ... so take a look at the thread previously referenced and let us know if the procedures are easier to follow now!

Originally Posted by Monkeyking

this morning after letting the car sit overnight for 8+ hrs, obd voltage was reported at 11.5 w/ the key in position 1 & car in park. after starting, voltage dropped to 9.2 & slowly increased to 13.8 at 800 rpm. on the drive in this morning w/ headlights on, the voltage was not as drastic as reported yesterday. remained steady at 13.0 when braking -> 13.8 at full stop. idle was at 13.4-13.9. driving was reported at 13.8-13.9.

i will be running the load tests this afternoon after work since doing this at 5am in the dark was not too feasible. thanks again everyone for all the suggestions & help. i will report back my findings.
cheers,
larry

Your voltage readings are what the alternator is outputting to the battery, which look fine.
Your battery is not charging which is why it is reading 11.5 volts.
You need a new battery.

Originally Posted by JimLev

Your battery is not charging which is why it is reading 11.5 volts. You need a new battery.

Heed JimLev's words!

Here is a picture of my battery, yesterday, at 5:30 am, after charging all night (taking 5 amps all that while) ...



Here is a picture of the $115 solution:


For more details than you probably want, see:

- One user's experience debugging a half-dead instrument cluster (1) which, after testing the fuses (1) battery & alternator (1) thankfully turned into an alternative battery search (1) and a simple battery replacement DIY (1)

Thanks for all the replies, advice and help. Been busy with work. To update. I measured on thr voltimeter 11.5 after sitting for 9 plus hrs. Car measured 9.7 cranking over. I picked up the duralast 49dl this past weekend and installed it in 30 mins. This is including the time for the car to go into sleep mode. It was pretty smooth. Went to start the car and at 1st would not hold an idle. After the 3rd attempt it was fine. Strangely the door locks were out of sync. Passenger door locked and would not unlock with the central unlock button or pulling on the handle. Pulled off the negative and replaced it after a few mins and it was fine again. Nothing lost other than time and date settings. On day 3 with the duralast and all seems well. Battery is at 13.9 at idle. 12.5 after 8 hrs via the voltimeter readings. Thanks again.
Cheers,
Larry

Originally Posted by Monkeyking

I picked up the duralast 49dl this past weekend and installed it in 30 mins.

Two questions since I put in the Johnson Controls Duralast 49-DL just yesterday:
- Pictorial discussion of charging, testing, removing, & replacing the BMW E39 battery with the Duralast 49-DL

Q1: How much did you pay for the Duralast 49-DL Autozone battery?

Q2: How did you route the vent hose extension so that it didn't get squished against the plastic panel next to the battery cross brace?

Originally Posted by bluebee

Two questions since I put in the Johnson Controls Duralast 49-DL just yesterday:
- Pictorial discussion of charging, testing, removing, & replacing the BMW E39 battery with the Duralast 49-DL

Q1: How much did you pay for the Duralast 49-DL Autozone battery?

Q2: How did you route the vent hose extension so that it didn't get squished against the plastic panel next to the battery cross brace?

Q1: How much did you pay for the Duralast 49-DL Autozone battery?

i paid 114 including tax. no core charge as i brought in an old spare battery as a core.

Q2: How did you route the vent hose extension so that it didn't get squished against the plastic panel next to the battery cross brace?

i did my vent host just like the picture below (not my picture or car). its not squished at all. i can post an actual picture of it later today.
cheers,
larry

Originally Posted by Monkeyking

i paid $114 including tax. no core charge as i brought in an old spare battery as a core.

That's exactly what I paid, and, yes, no $12 core charge for me either as I brought the battery with me.

I did happen to keep my old red plastic positive terminal cover from the old BMW battery - which turned out to be handy as it's MUCH nicer than the Johnson Controls flimsy orange plastic cover!

Originally Posted by Monkeyking

its not squished at all.

Hmmm... Mine is squished slightly.

QSilver7, in the thread below suggested cutting off a small piece of the black flimsy elbow on the battery end so that there is more room. Notice in my picture above and in the one below, that it's a little pinched.
- E39 (1997 - 2003) > Good Replacement Batteries for the e39?

Yesterday I got less excited about test #9. I was seeing lower readings, under 12V for a new battery. So I stop by the shop where I bought the battery.

They test at the battery itself -- full 12.6V! Maybe the cluster test isn't accurate?

Originally Posted by bluebee

Hmmm... Mine is squished slightly.

QSilver7, in the thread below suggested cutting off a small piece of the black flimsy elbow on the battery end so that there is more room. Notice in my picture above and in the one below, that it's a little pinched.
- E39 (1997 - 2003) > Good Replacement Batteries for the e39?

here are actual photos of my vent tube for reference. the vent tube is actually not squished at all.
cheers,
larry

Originally Posted by Edgy36-39

Maybe the cluster test isn't accurate?

I would think it more likely the cluster is accurate; and that the battery voltage is fluctuating.

Did you bleed off excess charge when checking the open-circuit voltage?
For closed circuit testing, did you load it?

I don't remember if you went to Autozone, if you have one near you - you might want them to check it on the car.
They checked mine, and said it was bad (and they were right), even though it was starting my car just fine.

Originally Posted by Monkeyking

here are actual photos of my vent tube for reference. the vent tube is actually not squished at all.

Nice. Very nice. That's a third way to route the vent tube:

• Pleiades' way (up over the top & then under the positive battery cover)
• QSilver7's way (cut 1/4" off the vent tube extension elbow)
• Monkeyking's way (up over the top and into the cell-cap groove)

So others benefit, I'll add your pictures to the existing DIY:
- Pictorial discussion of charging, testing, removing, & replacing the BMW E39 battery

I would think it more likely the cluster is accurate; and that the battery voltage is fluctuating.

I just got back from trip, and car started right up after sitting for nine days. Don't see how that would of happened if battery was discharged.

I didn't go to AutoZone, went to garage that sold me the battery. I watched him do the reading -- how should he have bled the excess charge?

Originally Posted by Edgy36-39

... went to garage that sold me the battery. I watched him do the reading -- how should he have bled the excess charge?

Here are several tips on how to "drain off" battery surface charge:

Also, when running TEST 9...I suggest ignition position 1 instead of position 2. At position 2...all the car's systems are up and running...thus there's an immediate and much larger drain being extracted from the battery. At position 1, there are fewer electronics activated...but yet...there is still a drain immediately on the battery. This is why you may see a lower battery voltage reading when running TEST 9 when the car has been sitting for a couple of hours...vs using a meter directly on the battery (when there's NO electronic load).

As long as you are above 11.89 volts...I wouldn't worry too much. Even still...on a new battery...there should still be enough RC (reserve capacity) and CC/CCA (cranking/cold cranking amps) to start the car even if the battery has dropped to 0% state of charge.