It could be your alarm but haven't heard of that problem before. My retired 08 535i had Increased Battery Discharge message when I first got the car in 09. The dealer replaced the Comfort Access main module (not individual door handles), the electronic gear shift and finally the after market 'Boomerang' alarm system was removed and the problems was solved. Usually the dealer can narrow down the problem if the car refuses to go to sleep after about 15 minutes.
Having said that, my car had two batteries during its life with me. I drove infrequently for short distances with few highway miles.

I have heard that the IBS can break down and cause problems. My advice still stands. Start with the battery change. If the message reappears move to the IBS and at least test it and then replace if needed. My 2 cents.

 

Here's my piece of experience. Battery change - maybe yes, maybe not neccessary yet (will be soon anyway if it's 07). Did those BMW guru's put it on diagnostic, so that IBS shown problem? If not, I would not change IBS yet. I was proceeding the same way (got 530iA 2006) -> High rate of battery discharge -> replaced battery -> still High rate of battery discharge, but no problems with IBS when hooked up with DIS Diagnostic - so no reason to replace IBS. Diag only showed problematic outside drivers door handle (got CA). You mentioned - you already went through this, so lets expect that the problem is not with Comfort access today.

I recommend to follow what was already mentioned:

- replace battery with new one
- let it register by someone with diag (easy task)
- check if it helped

1 Hint - ask the guy, who will be registering battery to check also error messages and search for IBS errors - once diagnostic is hooked up, there is no problem to check it. So if IBS will be mentioned somewhere, you can probably expect that replacing of battery will not solve your issue completly. Then you can trust what BMW guru's said.

Genearal comment - it's been written everywhere around the world (BMW forums) that when battery is low in BMW E60 - it could start to doing lot of weird things. I-drive freeze, DCS errors and many many more..

 

Just like everyone is saying here, it' really too easy and to be RIPPED OFF at the stealer for something so simple is pathetic. Autozone sell and exact battery. In my case there records show a different battery but this was an error and so look for the gold battery, I believe it's made in Germany as well. I was told the key is the cranking amps and cold cranking amps being the same. If the amps are different then you might need to be reprogrammed. I have the software to do this myself register and program. I went in an registered this but I am not so sure that it actually took. Either way this was all that I did and the problem went away. BTW the AZ battery comes with a seven year warranty and the stealer only a two. I have heard that if the battery is not properly coded/registered it will prematurely fail. So what, I will just go back and get another free battery and drink a beer while they are installing it!

 

Most cases this msg "Increased Battery Discharge" on 550 is door handle faulty.