E60 550i 2006
(Before I discovered the issue and ISTA, I changed the battery twice. Even after installing a new one, I still notice that the lights dim significantly when I throttle and start the engine barely each morning)

Just figured out ISTA and scanned for fault codes, got this:
CDA2 (power management, battery voltage 0x3B4) faulty, receiver DME, transmitter CAS/PM.
CDA3 (power management, battery voltage 0x334) faulty, receiver DME, transmitter CAS/PM.

E714 (Battery voltage, 0x3BE) faulty, receiver IHKA, transmitter DME-DD3
E716 (Consumer load, 0x3BE) faulty, receiver IHKA, transmitter DME-DD3
(couldn't find any solution or anything about those upper 4 errors)
ALSO
Maybe those also have relation?
E204 PDC:K-CAN-Low wire fault
E244 SZM:K-CAN line fault
E5C4 CID:K-CAN line fault

2F80 DME: System time, plausibility
+
Whenever i try to check on service function tab > voltage supply > evaluating the battery state of charge it shows the following:
Engine control cannot recognize IBS. This may be due the following cause:
.IBS supply interrupted
.BSD between DME/DDE and IBS (open circuit, short circuit, loose contact)
------------
I checked the IBS in the trunk and noticed that the positive lead was disconnected. The blue and black connector between the positive terminal and the IBS the wires inside were dusty. I removed it and connected the wires directly, and I noticed some sparking when I did. However, after trying to access the service function again, it still can't recognize the IBS.

From my research, it seems that a faulty IBS typically prevents the car from starting, but that's not the case for me. So, maybe the IBS is still functioning?
What to do/check? Any explanation about the following codes?

 

If your battery charging system is not cycling the battery properly, you will get a host of red-herring faults. Focus on the charging system first.

 

I have the same thing, the same errors, I can’t figure out what to do, changing IBS doesn’t help. How did you fix this?voltage 13.8-14. there are no other errors. the battery is new. wires from IBS to DME are OK. I don’t know what to do anymore

 

Check the battery charge status and charge status histogram. What notifications or codes are you seeing?

 

CDA2 (power management, battery voltage 0x3B4) faulty, receiver DME, transmitter CAS/PM.
CDA3 (power management, battery voltage 0x334) faulty, receiver DME, transmitter CAS/PM.
E714 (Battery voltage, 0x3BE) faulty, receiver IHKA, transmitter DME-DD3
E716 (Consumer load, 0x3BE) faulty, receiver IHKA, transmitter DME-DD3
2F80 DME: System time, plausibility
The charge histogram is equal to 13.8. at full load 13.4.
IBS I turned it off. If you don't turn it off, it drains the battery.
Fix it online, you don’t provide this service? All programs are on the laptop

 

Are you using ISTA / INPA?

 

yes everything is there

 

Post a screenshot of the Control unit tree.

 

Was this car a recent purchase? Looks to me like this did not happen over night and previous owner knew it had an issue but could not find what was going on. These things are hard to figure out over forums. If this was a vehicle recently purchased I would say you bought a project car that you had no clue was hard to actually diagnose. Issues like this takes a person who's physically at the vehicle that knows how to troubleshoot electrical issues. Saying that I would tell you to start reading up on the things I tell you because no one is going to be able to point you to the magic fix for your car especially if this is a recent purchase because I'm sure the previous owner spent a lot of time trying to figure it out.

I would first start by pulling modules and visually checking for corrosion (MPM, DME, CAS). Then I'd run a parasitic drain test to see if I'm getting a draw. Hope that you are because if you're not then you have to make a choice at this point. Are you will to spend money or let it go. I say that because you're going to need someone that specializes in electrical faults to physically look at your car since you are not strong in troubleshooting these sort of things or may not know how your vehicle actually communicates. To me it's telling you where to look. You just need the right tools (ISTA, voltage meter) and the knowledge to solve.