Battery Discharging Then All Hell Breaks Loose

[Motolord]

My 750ix has been telling me on and off for quite some time now that the battery is discharging when stopped or that it's low and it needs longer drives to charge it. While it doesn't get driven all that often (I've been working from home) I keep it in the garage with a battery charger connected to it and it's always run just fine. I don't know why it always thinks the battery is low.
The issue I'm suddenly having is I drove the car a couple of miles and shut it off. When I tried to start it there was a strangled clicking like the starter was dying. I waited a couple of minutes and got the car to start but every light on the dash came on and stayed on, and the iDrive threw me every warning I'd ever heard of and many I hadn't, Transmission Malfunction, Chassis Stability malfunction, Electronic Damping Control. The list goes on.
I got the car home and hooked up my code reader. There were codes all over the place. I cleared them out, shut the car off, and started it back up. It started with no issues. I did a real-time read and the alternator is putting out 14.2 volts. I put a multimeter on the battery with the engine off and got 12.6v. I put it on the charger overnight and the car was back to normal the next day.
Several days go by and the same thing happens all over again. This time I went to a place to look into getting a new battery. They connected a tester and said the battery was fine and it would be a waste of a lot of money to replace this expensive AF battery.
I don't know what the heck is going on. The only unusual thing is that my wife has been driving the 750 while I'm working on the "Alternator Bracket" oil leak on her X5. She doesn't like getting the 750 in and out of the garage so she leaves it parked in the driveway. It's been raining a lot lately. I suppose it's possible water got in somewhere but the issue comes and goes so suddenly it's hard to believe that if something got wet, that it got dry that quickly. Anyone experienced this or have any ideas?

[M_Bimmer]

I recommend you do the easy stuff first.

1. Check that your ground straps between the engine and body are still intact and not corroded

2. Depending on your codes, your Integrated Supply Module could be faulty.....

[Qsilver7]

Just curious..how old is your battery? Can you see the mfg date on one of the battery posts….or does it have a mfg sticker adhered to the body?

You can see an example of the mfg date engraved into a battery post in the pic below. The 16/20 means that the battery was MFG’d the 16th week of 2012:

[Motolord]

I don’t know if this has anything to do with anything but I discovered what appears to be water dripping from the turbo cooling lines into the engine valley. It’s dripping from where you see the corrosion on the clamps on the hoses.

[Motolord]

Qsilver7, there is a small round sticker on the side of the battery that has 06/18 on it. If that’s the sticker you mean the battery is from 2018. I don’t recall when I replaced the battery. I guess it’s a few years old, my multimeter and an auto parts store’s tester/analyzer indicate the battery is still good though. My code reader also indicates the alternator is good. However, I realize electrical stuff is super tricky and maybe it’s the battery but silly things have been happening with this car for a while.