the lights went all dim today. and the OBC said there is a 9.56 voltage going on.
on the terminal i measured 10,50 and so on both batteries.
i think it's the voltage regulator but what do you guys think

If you measured 10.5 Volts, you have inadvertantly opened the door to let all the electrical Gremlins in. You should be reading about 11.6V and higher at the batteries. The MID is probably giving you the correct voltage that the system sees. Get those batteries charged! If they are new, you may have a charging issue (bad diode in the alternator, etc). Doubt it is the voltage regulator...

last month mine did the same, the obc gave me now warning. the alternator was not giving any volts. 9 volts might be whats left between the two bateries on yours. mine went to limphome mode before it died. l was outside a autoparts retailor and had to buy 2 bateries, that got me home. I recharged them over night and took the car to a local auto electricians.
he overhauled it £50. +£250 labour. he had to remove the sump guard, the power steering pump, pipes from the radiator. it took him all day.
driving it home I smelt batery acid. th baterys were hot.I took it back,
16 volts. they striped down again this time fitting bosch parts and bench tested it. they warned me of a bad earth cable from the engine to the body. I told them to change it but keep the old one. I have never seen such a bad cable it crumbled in my hand. so i changed the braded LH one in the boot for good measure. Iv'e got a digital voltage tester now that plugs into the cigarette lighter. plug it in 12 volts ish. start the engine.
14.2 volts. happy days. The hardest £250 hese ever earnt

it's easier to pull the engine to get the alternator out , right?

Alternator on my 93: DISCONNECT THE + CABLE FROM THE TERMINAL BLOCK TO THE ALTERNATOR!!! loosen the power steering pump from the bracket, remove upper airbox half(drivers side), MAF, and hose to the DK. Remove fanclutch and fan, loosen tensioner, remove belt, loosen radiator hose at radiator (keep end of hose above the radiator!!). Now you should have enough room to get the alternator out. The biggest frustration was the single blue wire at the back of the alternator. I cut mine knowing that I will splice in a weather-proof connector to make it a bunch easier the next time. The "large" wire is easy to disconnect. You can either do it at the alternator or disconnect the entire "tube" from the intake runner (be careful, it is known to start engine fires!).
Installation is reverse of removal.

in my mind it sounded worse including taking the radiator out.

I would be willing to bet - the brushes on the alternator have given up.

Precisely the same thing happened to me last week while driving my wife's 735i. Many similar experiences over the past 30 years, have yet to purchase a new or rebuilt alternator, just replace brushes.

Last weeks failure: twelve bucks for a new brush set w/holder. Remove and replace alternator as described above (disconnect battery first), open the back of the alternator, scotchbrite to clean up the armature, remove old brush holder and replace with new.

Brad
1979 635Csi
1991 M5
1992 735i
on a quest for an 850i...

prairieman you hit the nail on the head.
i started with taking out the brushes because i remember checking the charging yesterday. (i do that from time to time) and it was 13.88v)
so what can happen from yesterday to today that changes the situation so fast.
i put in new bushes and it's charging fine again.
i have a spare alternator but i really didn't feel like huddling that mofo out.
thank you steffen
without your short way of doing the job i would not have done it today.
took me like 4 hours.
thank you all for your input.

you'll get faster at that, the last time I did it it was 20 minutes in and out.
Keep in mind though, that is with alot of practice and alot of Band-aids!!!
(The quick disconnect helps alot too)

20 mins? wow... i am not sure if i want to really want the need for the practice...
if you see what i mean.
right now i am happy for that the car is running another day
and that my girlfriend is going on about how much time i spend underneath the car
insted of driving....
and lucky me, she is going on about all of that in the other room.