[admins - this relates to my father's E39 530i not an M5 so please move elsewhere if neccessary]
Summary of story below:
- If a battery terminal is loose can it cause an alternator to fail?
My dad's car went into the bodyshop to have one side completely resprayed. When he got it back he noticed the clock in the car was not set right and assumed they disconnected the battery for some reason.
A few days later, after no more than 40 miles, he ended up with a warning light on the dash, a battery icon, followed immediately by trans fail warning (it's an auto) and he lost all power on a very dangerous and fast stretch of road that had no hard-shoulder. He waited for recovery, whilst waiting the battery was so low that the hazard warning lights wouldn't work after 5 minutes use and he couldn't gain access to the trunk to get the warning triangle
The RAC recovery arrived and towed him to a safe location then set about trying to jump start him. He then noticed that the positive terminal on the battery was completely loose.
He tightened it completely before attempting to jump the car. He then diagnosed that the alternator wasn't charging the battery.
The vehicle was then recovered to the local dealer (same chain as bodyshop that didn't reconnect the battery properly).
Diagnosis from BMW - the alternator has failed and it needs a new one (£600) and there's now way that could've been caused by a loose battery terminal according to them.
We asked for the exact problem with the alternator, they have just got back to me and said "something inside failed, we don't know what".
I did some quick Googling and found that a loose terminal could cause the alternator to run at 100% for a while or perhaps intermittent connection could make the alternator run on-off-on-off in rapid succession? If there is any evidence that a loose terminal could cause alternator failure please let me know so i can pass-the-buck when it comes to paying.