New Challenge:

2005 325i
68,5XXmi

Background:
Replaced OEM battery 2 months ago.
Car refused to turn over on Tuesday, took 4 attempts.
First 3 attempts just a click, no signs of attempted ignition. All internal/external electronics work (lights, turn signals, radio, a/c etc).
Final attempt, ignition.
From Tuesday until this morning I was getting mixed starts, strong/normal and weak. The weak starts sounded like a dead battery would.

Decide I'll take it to dealership to see if its the starter/alternater since the battery is still new, if not I must have a power draw sonewhere.

This morning everything is going fine including 4 cold starts with no problem.. get to the stealership for a once over, and the car isn't turning over anymore.
I get a jump box and it turns over fine.
Must be a dead battery, must have power draw?
Go to Autozone and get/install brand new battery.
No start there, even after installation.
Jump box, couple weak attempts and then ignition. Maybe the battery had to charge from sitting in the shelf?
Get back over to dealership, no ignition. Just electronic starts like the initial issue.
Check battery terminals, everything is secure.
Maybe the new battery is already dead somehow?
Voltage reader: 900/750cold amps or something, more than enough power.
Attempt to start car.. Click, click, click.
Maybe its the starter? Tap that a couple times. Nothing.

Lead tech thinks its a bad starter.
Secondary tech grabs a jump box anyways..
Jump box again, clean start.
No one knows how/why...


My idea, problem:
The car isn't pulling from the battery in the rear, for whatever reason (help!)

My idea, probable cause:
Power is only being sent for ignition from the front battery terminal and after the car starts, power is being drawn from the battery.

Theres something happening between front and rear terminals thats causing this or the ECU isn't functioning properly?

Probable solution:
No idea..

Please help, thanks