Just weird stuff happening
 

I have 2006 X5 3.0. 99k miles and has been very well cared for. Lately I've been having issues with fuel trim and bad 02 sensors. Changed them both and issue went away. A few weeks later, same problem. Removed catch can (long story about why that's needed) and cleaned it and replaced what appeared to be a faulty drain Valve. Problem solved. Drove it off and on for a few weeks (maybe 100+ miles or so in town) with premium gas. No issues. Today out of the blue it went into failsafe mode with 4x4 light on and 4x4 inop error as well as "yellow" brake light on. Scanned it and it threw aP0461. I cleared it and drove same distance, all issues came back. Scanned again and it threw P1500. All the time, no check engine light. When I went to check MAF (just in case), the whole bellows was loose and hanging off. I reconnected and tightened clamp, drained the catch can and reset ECU. Drove hard around block triple the distance and no issues, no codes. Could that have been my issue all along? And/or could a battery that may be headed south cause a lot of random issues?

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What scanner are you using? I found BMW specific scanners to be preferable to generics for the most part.
A battery going bad can cause all kinds of errors.
Others will have better opinions than I.

+1 on the BMW specific scanner.
P codes are generic and may equate to something totally different i.e. fuel pressure bank 1 but it's really "misfire" cylinder 1, they list the most common as the answer.

I swear by the Foxwell NT-510 or NT-520 but the NT-530 doesn't like to work on our e53's and the best thing is that it can stay in the car no matter the weather unlike laptop based scanners.

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Low battery volts will cause all kinds of headaches and false codes. If it's old, replace it. Charge it up now and then when not driven. A battery tender works great.

Bad MAF connections or air intake leaks will hurt short/long term fuel trims. The data readings will point to bad O2 sensors. P1174/P1175 indicate bad O2 sensors. P0174/P0175 are O2 readings point to vacuum leaks, bad plugs, MAF issues, and other items.