8R chassis, CAHA engine code.
My alternator failed, battery collapsed, recovered from M3... Local garage and Audi West London failed to ID the fault, so I did my own research (after the same failure again).
A. Replaced the 7 yo battery. Easy job, 10mm spanner to remove -ve then +ve terminals in the boot. Battery shd be the same spec, but you need to reprogramme the battery coding, for which you need VCDS (see Ross Tech forum). In theory you need to keep some power on the terminals under the bonnet to keep memory.
2. Use VCDS and run auto scan. CAN 19 measuring blocks 14, 15, 16 will give you Generator data (18, 19, 20 for battery)
I had block 15 error in Electrical Generator status
You can remove the regulator (VR) from the back of the Valeo alternator, but Q5 is tightly packed and you have mm' s to spare. Remove negative from battery (i didn't bother with a memory saver, no ill effects). Remove live from back of alternator, and plug... Take off cage with screwdriver. M7 to remove 3 bolts, remove VR.
My brushes were gone, check out YouTube for an easy soldering job to replace...
Wasn't my brushes though, then replaced the whole VR, not that either...still got the Group 15 fault.
Just embarking on replacing the whole alternator. Again doable..but you'll need some dexterity.
-Ve disconnected. Remove timing cover. Remove 2 bolts on coolant tube (black hard plastic), move gently sideways. Mark ribbed belt direction. Use a wrench on the tensioner to remove the belt from alt pulley only. Remove two screws, with a 13mm ratchet, on alternator bracket. Use a 19mm socket and a bolt to draw the alternator bushes out, its v easy . Bottom screw can not be fully removed, only once the bushes are withdrawn.... Audi service manual suggests tapping them out with a hammer - waste of time.... Remove the alternator from engine bay pulley first
And...Valeo and Bosch are not interchangeable...diff plug for starters.
Hope it helps