Originally Posted by BimmerFan52

The two key functions of the IBS are the DME wake-up function and the control of recharge voltage.

After the engine is shutdown the DME takes recent history of the battery SOC (state of charge) it holds and transfers it to the IBS memory and then goes to sleep. The IBS also sleeps, but wakes up every 40 seconds for a fraction of a second to take a snapshot of negative terminal voltage and exit current in order to update the SOC. If something is drawing power and the SOC is dropping the IBS can send a signal to the DME and wake it up. The DME can then force a shutdown of systems (radio, lighting, etc.) that are drawing power. The goal is to preserve enough charge in the battery to enable starting.

During engine and alternator operation the IBS measures the temperature of the negative battery terminal (with the objective of also measuring battery acid temperature). If the battery is charged with an excessive voltage during high acid temperatures the battery can experience excessive gassing, grid corrosion and removal of water in the electrolyte. The terminal temperature sent regularly by the IBS to the DME is used in an algorithm to determine the optimal output voltage that should be sent by the alternator to the system to minimize these side effects of charging and extend battery life.

Incidentally, this optimum voltage can vary significantly between FLA and AGM batteries. An AGM should never be charged with more than 14.6-14.7V, whereas the FLA can safely see up to 15.5V on recharge (again depending upon acid temperature). This is why if you replace your battery with exactly the same type it could be argued that reprogramming is optional, but if you change from FLA to AGM, not registering the battery could lead to very short battery life.

Originally Posted by paul-g

great explanation, I replaced battery with another excid. I went with the exact same spec one that the OEM one had and that excid suggest. The problem with the IBS is that when it goes bad it draws power and doesn't relay info properly so battery doesn't get a good charge. I also read they can get on the frits and work and then not work well so again will run for a while as I still right motorcycle in (prolly most of this week) and see how it is.

on a side note bmw also realized if their cars stay parked for more than 3 days the battery draw is large enough to pose a problem. car never really sleeps SO that's why it's good to replace this IBS if it's bad. just a small level of protection....for $200 lol

Originally Posted by paul-g

well only errors i had gotten was "high battery drain" and only 1 time " moderate battery drain".

Originally Posted by BimmerFan52

Errors as dash lights or did you scan?

Originally Posted by 6825786

Hello all,

My 545 is inside a heated garage. I have noticed that after 7-10 days of not starting it, the car feels just a bit strained to turn over. The battery is 2 years old and I have already replaced dthe alternator and tested the voltage. All is fine with the charging system. I know these cars draw a lot of power , even not driven.

i am going on a trip for 3 weeks. If I disconnect the IBS for that period of time, do you guys think I will retain more of a charge when I come back?

Originally Posted by paul-g

Bmw knows/says that car never totally sleeps.if u get 7-10 days lol and still starts i think ur good. I might put a trickle charger on it