If you have the radio located in the back or front is determined by if you have the navigation screen or the MID. What would be helpful is knowing if you have nav or MID set-up.
If you have onBoard nav (and screen) then the radio receiver is located where you looked (next to the battery). If you have the MID, then the radio is integrated into the indash single CD player (or cassette player in older BMW models)
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The MID is oft misunderstood to be (or called) the "head unit"...which it is not. The MID (multi-informational display) is just that...a simple display control unit that puts control of multiple systems into one component. The MID performs no calculations of it's own. It just receives information from the various systems (audio, OBC, clock, phone, DSP, etc)...and allows you to control the system you have called up.
If this is what you have (the MID)...then the radio is NOT in the back next to the battery...it is incorporated into the single CD or Cassette player that is above the MID:
{if you have the MID pictured above...then the radio is incorporated into the CD43/CD53 or C43/C53 mounted above the MID}
