Hi all, a couple of weeks ago, I noticed a strange whining (engine speed related) sound coming from under the bonnet, which lasted a few days then stopped.
Fast forward a few weeks and I've started having some, what appear to be, battery related issues.
First problem was the battery went totally flat on a short journey, so I assumed it had been an accumulation of short journies and the cold weather. Got it jump started and managed to get it home and onto charge through my C-TEK charger. This seemed fine, but closer observation of the voltage on my IIDtool showed the voltage was on 12.6V and once again after a short journey the battery was flat.
After it was charged, i put my multi-meter on the battery and it was showing 14.xV, so all looked fine. I then took it on a slightly longer journey a few days later and i constantly monitored the voltage as I was driving via the IIDtool. It started at 12.2V and gradually dropped to the point, just as I got home, where the car lit up like a Xmas tree and wouldn't even turn over, the IIDtool showing 9.6V!!!
My thoughts are that the earlier noise could have been the voltage regulator on the alternator failing, as described by other threads but I've also learned that the alternator is "smart" and will only provide the amount of voltage the battery will accept.

So the $1M question is, should I be looking at returning the battery under warranty, or consider an new alternator, or, if possible, just the regulator?

Cheers in advance. Got - 2017 SDV8 Autobiography in Loire Blue
Had- 2008 TDV8 Vogue SE in Java black
Had - 2007 S/C in Stornoway Grey

Not sure how smart our alternators are? Mine started veering between 11 and 17 volts which oriduced some interesting results! Our cars are particularly sensitive to incorrect voltages and your issues do suggest to me that your alternator is at the end if its life.