Search cluster test...solidjake has a youtube video of how to do it...that'll give you your voltage of the car when off and on.
Give the battery disconnect a try...but first, see if the cables on it are tight or not...shop might have disconnected them and forgot to tighten them up...who knows?
Debut Radio Show Tuesdays from 1-2-ish p.m. EST on Hamiltonradio.net The Mechanical Animals
call in for car repair help! 609-503-4058
A recent set--NSFW audio: https://youtu.be/_dcxcZfD6dg
Mangofy your E46!