It finally happened... Stranded battery woes

[Andyh1]

Tonight as I was heading out to the gym for a long swim.. My Z left me stranded.
Part of it my fault. I have been around BMW's long enough to have known.

The story :
Engine began to loose power, and the car kept struggling just make it out of second gear. The battery icon had been coming off at cold start up but then it would go away.
I managed to turn around to head back home but the M just died.

Here is the sequence for future records:
10 minutes after leaving my house the engine begin to hesitate.
It got worse as if it was about to give up the ghost but then it would come back on. 1 minute later instrument panel went crazy, lights flashing. Then I lost all exterior lights.
2 minutes later the engine was barely hanging on and 1 mile away from home, the car died as I was trying to make it back into my garage.

The battery icon had been coming on at every cold start up for about 5 minutes but then it would go away.
My fault for not checking it.

The tow truck driver got us home safely and helped me jump start the M.
Engine fired up fast but died quickly 2 minutes later again.

Throw me some recommendations on a new battery.
Probably did not help that it was cold in Houston tonight.

[Finnegan]

Man that sucks. On the plus side, it's not the ECU or some module that would far exceed the cost of a new battery!

[Andyh1]

Originally Posted by Finnegan

Man that sucks. On the plus side, it's not the ECU or some module that would far exceed the cost of a new battery!

Agreed.. I kept thinking that maybe it was the alternator but the engine fired up during the jump.
I'm only sitting at 30K

[Efthreeoh]

It sounds like you still may have an alternator issue. The engine should keep running once jump started even with a dead battery.

[racerbruce]

Presuming the tow truck winched your beloved Z onto a flatbed.
How old is (was) your battery?

[wdb]

It's possible for a battery to be bad enough that the car won't keep running even with a good alternator. In your case it sounds like battery replacement is a good first step, but get the charging system checked out once you've replaced it.

I recently -- and finally!-- figured out that my CTEK battery tender was not being put to full use. I had it on the Z4M and it never indicated a completed charge cycle. I never worried about it because the car always started and ran just fine.

Recently I picked up an E93 with a less-than wonderful battery. I hooked up the CTEK to it, activated the charging program for AGM batteries, and darn if that charger didn't restore the battery! It took quite a few days of constant charging for it to complete the process, but still -- wow. So I used the AGM program on the Moupe battery and, wonder of wonders, it restored that one too.

Moral: get a good battery tender and use it correctly.

[The HACK]

Originally Posted by wdb

It's possible for a battery to be bad enough that the car won't keep running even with a good alternator.

I'm not so sure about that. Once the car cranks, with a good working alternator, you can physically disconnect a battery and the engine should continue to have enough spark to keep turning.

OP's symptoms are consistent with a failing alternator. I've had a failed alternator on an '84 Maxima and a '91 318is and the symptoms are almost exactly like that. The Maxima even made it within 1 mile of home, died, my brother and I walked home to pick up a spare battery, plopped it in, fired it up and only to have it stop running at the foot of our driveway. It was a steep driveway too.

On the 318is I got lucky, because I knew the alternator was dying. My mechanic had told me that it's time to replace it before it stranded me. I noticed a HARD crank first, then got to where I needed to go for dinner that night, then it didn't have enough power to crank...But supplied enough power to keep the engine running for a short while once I was able to bump start it. You should have seen it, me pushing the car down a slight decline, got hopped back in the car, put it in 2nd and popped the clutch. The battery had enough power to keep the engine running, but not enough when the headlight is on. It was creepy driving the 5 miles home in the dark w/o the lights. The second I turned on the lights the engine dies.

[wdb]

I was thinking about a battery with a failed cell that might cause less than necessary voltage, even with an alternator. But you're right, the symptoms could point as easily to the alternator being the culprit.

[Andyh1]

Battery is about 3 years old, so I'll replace that first and have the alternar checked along with the rest of the system. I was taking to a good buddy and he also pointed to a failed alternator.
I'll deal with all this when I get back.. Taking the family on vacation.
The Z made it into the garage safely....

Thank you for the input... Happy Thanksgiving everyone!

[SD ///M4]

Letting the battery run down in a Z4 can cause major problems. When I had my knee replacement surgery in May 2017, my Z4 M Roadster sat for 3-4 months while I was recovering (I was able to drive my M4 but I couldn't bend my leg enough to get down into the Z). When I was able to drive it again I experienced trouble starting, random stalling, a loss in power, and problems with the audio system. I put it on a battery charger (which I should have done initially) and took it to my independent mechanic to clear all the codes. He warned me that I should never let the battery run down in the car. There are modules that can cause problems and fail from low power situations.

Bottom line, once the battery regained a full charge and the car was driven semi-regularly, all of the problems have disappeared. This was spring/summer last year.

Your independent can run a battery test to determine whether it needs to be replaced or not, or whether it can be recharged.

[Andyh1]

I wanted to throw a quick update here :
The car has been sleeping this winter with battery completely removed, after this incident. I got me a new AGM battery this weekend, fired her up and the car came to life. Radio worked, stations were still programed. All exterior lights were 100% functional.
I placed a volt meter on the battery terminals and got my readings :
Fluctuating between 12.28v-12.29v...i left it on for 1-2 minutes.
Time for an alternator replacement next month. New battery is being taken care of by my new Noco Genius G7200 battery charger.