battery gremlins N55 E90

[smadasam]

I have been having problems with my E90's battery.

Symptoms:
It would take a charge using a float charger directly on the battery. It would drive ok for a day, but if I had to start it too many times in the day, it would need a jump. I

important details:

• I replaced the led-acid battery with an AGM battery, which I though was my problem to begin with. I replaced the battery one more time with a new AGM battery, and this time correctly recoded the battery in the car for the AGM specs. I figured it would be then end of the problems, but no.
• I have had the motor replaced around the same time the battery has been giving me problems. i figured maybe it might have been a grounding issue, but it looks like the main engine ground on the left rear side of the motor is well connected, so the motor swap is suspect, but I am not sure how.
• When the car doesn't start, everything powers on, and I hear the fuel pump pressurizing they system in the tank, but the starter doesn't attempt to start
• I have never been able to successful jump the car from the terminals in the engine bay, but it has been able to jump on the battery directly
• At some point in this process, the FRM module burned out, and I replaced and reprogrammed it. This may just be coincidental.
• A new battery works for a while, if I float charge it over night
• currently it is dead in the water. Last time, I coudn't get it to jump even with a 40 amp jump box. Also, the cable from the jump terminal to the starter got very hot, like too hot to touch, so I stopped trying
• After this last incident, I was able to measure ~14v on the battery, jump terminal on the engine bay, alternator, and starter (without anything plugged into the system), so it seems like the voltage is getting everywhere.

I don't mind buying replacement parts to get the car working, but I don't want to waste money buying things that aren't the issue.

Maybe it could be the:

• battery distributor, https://www.fcpeuro.com/products/bmw-power-distribution-box-with-fuse-61146971370
  but, seems like if it were broken, I wouldn't get voltage to the engine
• maybe the power wire to the starter might be damaged: https://www.fcpeuro.com/products/bmw-cable-alternator-starter-base-b-plus-12427611316
  like it isn't completely broken,because we do see 14v down stream from it, but like it is comprimised and causes too much resistance
• or maybe the IBS? https://www.fcpeuro.com/products/bmw-battery-lead-negative-ibs-61127616200
  but, I can program it
• or the other battery wire? https://www.fcpeuro.com/products/bmw-battery-cable-plus-pole-sbk-61129130313

I would appreciate any troubleshooting tips to narrow this down.

-sam

 

[doublespaces]

Has the car ever been in an accident?

There is something called the BST, during an accident this pyrotechnic charge will attempt to sever the battery connection. Sometimes people refer to it as a 'fuse' in the pack on top of the battery, but if there is a problem with this you can get an inconsistent charge under very odd circumstances creating behavior that seems like your alternator isn't charging the battery. This is unlikely but this happened to me a long time ago and it took me a while to figure it out.

 

[smadasam]

It hasn't been in an accident that I am aware of. Is that on the positive side? I was reading maybe the cable is loose in that case.