Caution on fully charging bmw e70 battery

[Crowz]

I figured I would share my experiences with bmw's stupid battery charging scheme.

This only effects models that have the alternator that is controlled by the dme.

To quote bmw :

Instead of boosting idle speed to continually
maintain a desired voltage, the ideal energysaving strategy is to make it acceptable for a battery to partially discharge during extended
idling on the assumption that it can be quickly
recharged once the vehicle begins moving. This
saves fuel, but not allowing discharge to
go past the point where the engine can’t be
restarted is an equally important part of this
strategy. Only under DME control, with continuous battery monitoring, do such advanced
charge/discharge strategies become possible.

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Now to why its annoying me

Ive owned my 2013 e70 a few years and never had any problems. One night my wife and I went to jacks's to get something to eat. While in the drive thru I noticed my dashcam was turning off and on every few seconds. It makes a chime noise is how I knew it was happening. This was after being stuck in the line for 40 minutes.

I figured the dashcam was messing up since its a few years old. Its always had issues charging the camera when the cars running. I had even upgraded the dashcams onboard battery in hopes of it doing better which did help some.

Anyways for some reason I decided to call up the voltage levels on the p3 meter I have installed for monitoring water temps and low and behold Im seeing 11.5 to 12.1 volts. Varying a bit.

So I figure its alternator time. So I get home and put the car back on the charger which it stays on all the time anyways (all of my bmw's live on the charger network I built at the house).

I ordered a new alternator from fcp euro and when it arrived I installed it. That was NOT fun at ALL. Took all day. Nightmare city, hardest alternator install Ive ever done and Ive done a ton.

Well after getting this done I fire it up and guess what its charging the same as the old one. Grrrrr.

I then figure I must have a bad ground strap. So I bought a nice long negative cable and went from the alternator mounting bolt to the negative jump off point under the hood. Didnt charge any better. But it did seem to crank faster starting the car

Well I was pissed at this point to say the least so I didnt put it back on the charger. After 2 days I drove it again and it was charging perfectly. 14.4 volts to 14.8 volts.

Hmm.

Few days pass and still doing great. So I put it back on the charger.

Next day its not charging again. Let it drain back down sitting a few days and its back charging perfectly again.

I charged the battery back full again and this time took it for a long test drive. It stayed around 12 to 12.2 volts for an hour or so stop and start traffic and idling too. The it finally creeps up to 12.5 then 12.8 and after enough driving around its in the 13's.

After stopping for awhile its back in the 14's.

From all of my test as long as the battery is 12.5 or less it will charge as expected. Otherwise it uses the battery to run things to save gas or whatever till it uses up enough of it to go back to acting normal charge wise.

I figured I would pass this along in case someone ends up with aftermarket radio problems or other accessories they add. All of the bmw factory equipment seems to be designed to deal with the crazy voltage ranges.

No error codes, no warning lights, just crappy power management.

Also remember a fully charged battery is 12.73 volts or higher non loaded.

My e70 likes to keep the voltage when not running around 12.38 to 12.43 non loaded.

I guess I should of figured something was up since in all the years Ive owned it the parked charge seemed lower than I liked. The app I use to monitor all of my cars always showed it lower than everything else I own.

Friends Ive got to test their cars on this have had the same results. One wierd side not though if you put a china made cheap alternator on (not my e70) it will default 14.4 all the the time. Unfortunately it will shorten the life of the battery.