Update: After poking around with the multimeter a bit more started it up to test the battery at idle again. OBC was reading 13v steady! Took it for a drive and after around 2min it went back to the 11v range again.

Could be a loose connection somewhere? Or possibly heat related?

__________________
2001 E53 4.4i M62 [10/2000]
Topaz Blue / Montana Grey
Sport Package / Aero Kit
Winter: 255/55/18 Toyo Observe GSI-5 on Touren TR9
Summer: 255/50/19 + 285/45/19 Bald Rubber on Style 132