Battery and charging system experts please chime in

[generx]

Earlier this year, I replaced my alternator due to the dreaded battery light and posted a DIY here

Everything has been normal until last weekend. The battery light came on while we were about 170 miles from home at the coast over the weekend while driving on the beach. My first thoughts were WTF? Turned off the ignition and re-started the car about 4 more times and the light stayed on each time (constant on, not blinking)

Battery is 2 years old (OEM)
Alternator is pretty new

Made a beeline for a local auto parts place and bought a cheapo meter and got a 11.9v reading while running and 12.4v with the engine off. Drove back to the beach house 10 miles away with everything off, luckily it was still daylight.

Disconnected the battery and contemplated my next step (luckily I always carry a tool kit, garbage bag, and duct tape when driving long distance in any BMW) I re-connected the batter after about a half hour and re-started the X:

NO BATTERY LIGHT!

Checked the voltage while running and it was a healthy 14.3v. Was really tempted to keep the X running and drive straight home but it was getting dark and did not want to get stranded in the NW coastal range at night so decided to stay until morning. Locked it up and crossed my fingers that all would be normal the next day. In the morning, packed up and went out to start up the X, no battery light. Drove straight home and everything seemed normal.

The next day, went to a local Battery Exchange where they tested the battery and charging system under load, everything checked out normal, the OEM battery seemed to have normal voltage but the tech mentioned that the battery's amperage was about half of where it normally should be and that they could charge up the battery overnight. He also thought this was odd considering I just drove long distances the previous weekend. I declined and ran some errands hoping that the problem would re-occur.

Indeed the battery light came on again later (a constant on as usual, not blinking) Turned off the X and re-started it, battery light was off. I bought a new battery (from Batteries Plus) that day and installed it. My thoughts are that the 2-year old OEM battery is somehow defective or has a damaged cell(s) from a previous discharge cycle. Checked all connections/ground when installing, no corrosion. Everything seemed normal.

I'm really stumped at this point and paranoid that it may be the DME. I have no FSR issues, nothing is discharging the battery when it's not running, no warning lights, nothing.

Anybody have any thoughts on what could be causing the problem? It's been a couple of days and no battery light though. Could it have been the bad battery refusing a charge from the alternator? (does the DME cut off the charging system from charging a bad battery?)

[faz]

Not an expert by any stretch of definition, but just to let you know, on my motorcycles, I have had batteries that went bad on me after a few months. I even saw one that was damaged due to using a philips screw driver (instead of a wrench) to tighten the battery connectors. (I provided a new battery to the buyer, he put it on himself later on, and called me to complain the battery was tested bad after a few months.)

Perhaps having a new battery with an old alternator (prior to you changing it) damaged the 2 year old battery?

Hope that is all your problem is.

[motordavid]

I am assuming your car is still under warranty?
I would haulazz for the dlr and have a good tech
check it out.

Could be a bum battery, (even oe), alternator, a
drain, etc. But, if you are under warranty, the worse
they can do is beat you on a new battery.

Fwiw, any/every new battery is already weak when
one buys it; if you do get one, a trip home is not
the way to get it up to full snuff, imo. An overnight
low amp "trickle-type" charge is, imo.
GL.mD

[generx]

Originally Posted by faz

Perhaps having a new battery with an old alternator (prior to you changing it) damaged the 2 year old battery? Hope that is all your problem is.

Possible, it did go flat a couple of times from lack of use. I use battery tenders and also made sure that the OEM battery was charged up after installing the new alternator and everything seemed okay afterwards.

Originally Posted by motordavid

I am assuming your car is still under warranty?
I would haulazz for the dlr and have a good tech
check it out.

Could be a bum battery, (even oe), alternator, a
drain, etc. But, if you are under warranty, the worse
they can do is beat you on a new battery.

Fwiw, any/every new battery is already weak when
one buys it; if you do get one, a trip home is not
the way to get it up to full snuff, imo. An overnight
low amp "trickle-type" charge is, imo.
GL.mD

Unfortunately out of warranty. I also made sure to charge up the new battery (got a green light from my Deltran Bettery tender after a quick overnight charge --I use quick-connects on all my cars so I just plugged it in when I got home)

[motordavid]

generx, Sorry to read of no mo warranty.
And, good job on the Batt Tender. I'm thinking
it is something affecting your batt, but past
alternator or a glitch drain somewhere in your
system, I am no electrical/electronics troubleshooter...
But, Good Luck. mD

[X5girl]

You have a bad connection to the alternator or a bad alternator. Check all the connections and if they are ok, replace the alternator.

[Bill K]

generx, I noticed that you posted the alternator was new. Was it really a FACTORY NEW alternator, or was it a "new" rebuilt alternator? If rebuilt, then it's bad. Sounds like the voltage regulator or worst, the diodes. Either way, that alternator (typically, they have warrantees) should have a warranty. I've had the same issues a few months after installing a factory REBUIL alternator. It came and went, then it went bad alltogether

[ika]

check belt tensioner..
maybe altrernator voltage regulator problem. I had same symptoms on mercedes c-class, sometimes alternator light was on.
after couple of dayes light stayed on and battery was drained. just replaced regulator..

[generx]

Originally Posted by X5girl

You have a bad connection to the alternator or a bad alternator. Check all the connections and if they are ok, replace the alternator.

All connections were checked and free of corrosion. Alternator was replaced in January of this year.

Originally Posted by Bill K

generx, I noticed that you posted the alternator was new. Was it really a FACTORY NEW alternator, or was it a "new" rebuilt alternator? If rebuilt, then it's bad. Sounds like the voltage regulator or worst, the diodes. Either way, that alternator (typically, they have warrantees) should have a warranty. I've had the same issues a few months after installing a factory REBUIL alternator. It came and went, then it went bad alltogether

I replaced it with a brand new Bosch alternator made in the USA with a lifetime warranty. There was just no way I was going to go with OEM which went bad at 50K miles (the OEM one was bench tested and failed all 3 tests)

Originally Posted by ika

check belt tensioner..
maybe altrernator voltage regulator problem. I had same symptoms on mercedes c-class, sometimes alternator light was on.
after couple of dayes light stayed on and battery was drained. just replaced regulator..

Tensioner/belts are all good. I may have to pull the new alternator again and get it bench tested just for peace of mind.

[X5Flyboy]

battery life seems to be one of the more common problems with the X5 - it is a real electrical hog - there is always a drain - am entering my 5th year with this OEM battery - I ALWAYS shut off everything I can before turning off the ignition, including the NAV screen - anytime I don't plan to drive it for more than 7 days, I hook up the BMW battery trickle charger - so far, so good - but it gets replaced at 5 years, need it or not