Odd...I just noticed today that the radio was on mute when I started the truck on my way home from work. It only lasted maybe 1/2 second, then it was normal. I did't think anything of it, until now. Ive had no other symptoms of low voltage.

OK, so I now have a warning message saying: "Increased battery discharge! - Vehicle battery. Increased battery discharge while statonary. Electrical consumers may have been switched off. Reset date and time if necessary. In the event of recurrence, have the system checked by BMW Service."
How can I know this is the battery that is slowly dying? Could it be something else that discharges the battery? Or am I not driving long enough distances (as Nanniepoo suggests)? I don't drive much and it's often very short trips... I'm happy to change the battery, but I'm hesitant to take it to the BMW garage, since they are very expensive just to do a diagnostics...

Electrical system diagnosis is not my forte unfortunately.

I just got the car, and it started with warning me if it sit for a while, or the car wash thing. Now it's every time because of the short trips. Got some highway time in yesterday and although it still shows a warning, my clock stays set and comfort access works.

I've also had a CEL all week. Scanned for codes yesterday and apparently there was none... I can read live data so I'm assuming my scanner is hooked up fine. I know low battery shouldn't set a CEL, but I'm hoping it's causing some other complication.

Is the 'battery' the Chupacabra of the E70 world?

(Everything bad that happens is the battery.)

Want some advice?

Change the battery yourself, THEN go to the dealer. Ask them to check the CELs and register the battery.

Mark my word you dont do that you will get trapped into $200 diagnostic and then $600 for a battery

Though a low battery may cause radio muting (and other issues) this is not the case in my instance. The radio is actually on but the volume is at the lowest level. Once I turn up the volume everything is OK. I am sure there is some feature or trick that I haven't figured out yet.

Came out to $360 ($245 for battery, rest labor/fees). Obviously more than doing it myself, just a little gun shy with the new car and all the fancy software. 95% of my DIY work has been on an E36, which I feel is a pretty straightforward car. Main gripe is it took 2 hours because the car wash was backed up lol. They did do the multi-point inspection. Noticed a valve cover leak and timing cover leak, although I have yet to notice anything below the vehicle, any smells, and after the 4k miles we've put on it, oil level has not dropped via the computer, so it'll be left alone until there's an actual problem.

The CEL disappeared Saturday morning. I spent about 2 hours on the highway Friday so things definitely had time to charge up. Also stopped at an O'Reilly's and their reader also came back with no codes. I forgot to ask while I was there for them to scan to see if anything is lingering.

Radio starts up however it was left (whether mute or on), so I can testify there's a direct relationship.