Test DO NOT GUESS.
Tools Volt meter (digital) after confirming all the posts are clean and tightened including all the grounds in the trunk area. This will confirm no water in the well, positive cable has NOT been compromised by the explosive connector.
Read/Test at battery post in the trunk
first. Reading engine off over 12.5 V?
Start engine, Read at battery posts. Over 13.5V?
Do a Voltage drop test on the cables. See image below. and video
https://www.youtube.com/watch?v=3-9oZuX6-Pg
Move to under hood jump post +, tight? Read Voltage engine running...over 12.5V and steady? Bring RPMs to 2500, reading?
Turn on all the accessories while reading voltage. Still above 13.5V? Steady? bring RPMs up to 2500. Steady or moving all over?
The RPM tests show regulator function with speed and load. Most of these alts die due to the regulator loosing connection at the slip ring or the reg going dumb. The voltage will bounce all over the place.
Options: If everything points to the alternator then look at the back of your alt and buy a NEW not rebuilt unit (Bosch or Valeo) unless you are willing to install and reinstall until you get a functional one. See all the other postings on charging issues and rebuilt alternators for examples of those who have tried the price path before you. Cheap is not the way to go. But as they say, it is your car, time, wallet, etc.....
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2005 X5 4.8IS
The
Blue ones are always FASTER....
Current Garage:
2005 X5 4.8is
2002 M5 TiSilver
2003 525iT
1998 528i
Former Garage Stable Highlights
2004 325XiT Sport
1973 De Tomaso Pantera, L Model
1970 Dodge Challenger T/A 4 sp Alpine White
1970 Dodge Challenger T/A 4 sp GoManGo Green
1971 Dart Sport, “Dart Light” package
1969 Road Runner 383
1968 Ply Barracuda 340S FB Sea-foam Green