I purchased this vehicle in October 17, 90 thousand original miles 3 different owners according to carfax. Car was in perfect condition, I personally kept in garage and rarely got out for the first couple weeks then I decided it needed some sound, so I had a 4k stereo system installed by experts of course. I personally thought the guys did a good job even though I asked for front and rear cameras just for the heck of it. The installed a Kenwood double din dash unit 2 kicker comp 12's and two kicker amps one is the KXA400.4 for my mids and highs the second is the 1200.2 for my subs full box enclosure with lit plexiglass back that comes on with the trunk and put the amps where the spare tire would go. Looks really nice. I noticed somethings not working steering wheel no longer telescoped, seat no longer moved forward or back, and a horrible buzzing sound at low volume so I take it to certified BMW center to have a tune up. They come back with 5k worth of stuff that needed done some critical some not so much I had them fix the critical stuff which was rings, seals, brakes, ect. I pick it up a week later and was driving for the second or third time and Im on an on ramp getting on highway and im having a little fun and my wife heres a hissing noise then my check engine light came on and stayed on. I called my tech and he said bring back in well I was couple hundred miles away for Thanksgiving and I couldnt so when I got back to KC they said I had put to many miles on it to guarantee thier work. I said ok no biggie. Then my wife and I were out for a cruise and the battery light came on, we headed home and got almost there it dies we walk back to house put some cables on it got it home back in garage. First thing I check is battery it read 12.7 give or take a point. so I went and bought a bigger battery with the system and all the bells and whistles thought maybe it just didnt have enough to keep up, still shows battery light, then I charge battery run to advance auto parts and them boys touch the post on battery and they tell me its a bad alternator 416 plus core bc its water cooled. and my alt is only putting out about 8 volts so I order a an alt and have some guys over to help and they all think it might be bad wiring or bad ground loose connections so before tearing into this they wanted to troubleshoot. We found no indication that the new batter was bad but did find the old battery wouldnt hold a charge so at this point we are all thinking that it was just the battery. We tried everything from using meter while car is off then starting it, then turning everything on and the volts just dropped, everything seemed like the alt was bad and all of us are thinking what are the chances of the battery and alt going out at same time. So we start checking fuses and find that there is no fuse in the slot for the charging socket so i put a fuse in there still showing battery light after this long story my question is should I go buy the correct smaller battery and a capacitor and see if the capacitor I will hold a charge? Or just bite the bullet and get new battery, capacitor, and alt. Or should I take back and demand that either the stereo shop cut a wire or the BMW shop and pay a fortune? OR Is it just replace alt and see what happens?