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Old 01-14-2013, 09:51 AM
fun2drive fun2drive is offline
BMWCCA 149159
Location: Panhandle of Florida
Join Date: Nov 2005
Posts: 2,866
Mein Auto: 17Ridge/14JGC/ 17Outback
This is what the IBS does from the training publications the techs receive. I am looking for the detailed write up and will post that when I can find it but it is a lot more complicated than it need be.

Intelligent Battery Sensor - The IBS is a mechatronic intelligent battery sensor with its
own microcontroller. The IBS is connected to the negative battery terminal and is used to
measure battery terminal voltage, discharge/charge current and battery (electrolyte) temperature.
The information collected by the IBS is used to determine battery SoC and
SoH. This information is sent to the DME via the Bit Serial Data interface (BSD).

The IBS contains a micro processor that is used to monitor/measure various battery conditions
such as:
Terminal voltage via measurement from B+ to Gnd
Charge/discharge current via integrated shunt resistor
Temperature of battery acid via integrated temp sensor
Index Explanation
1 Battery Ground Lead
2 B+ Connection for IBS
3 Bit Serial Data Interface (BSD)
4 Intelligent Battery Sensor (IBS)
Index Explanation
1 B+
2 B-
3 Battery Voltage Measurement
4 Battery Temp Measurement
5 Current Measurement
6 Microprocessor

IBS Measuring /Evaluation Function
The measuring/evaluation function of the IBS electronics, continuously measures the following
values under all vehicle operating conditions:
When the vehicle is stationary, the IBS is programmed to wake up every 14 sec. and
makes the required measurements within approx. 50 ms in order to save power.
The measured values from the IBS are provided to the DME by way of the Binary Serial
Data Interface (BSD) to calculate the State of Charge and State of Health for the battery.
State of Charge (SoC) is a calculated condition showing the current charge of the
battery. SoC is used during key "OFF" periods to insure the battery maintains a sufficient
charge to start the engine at least one more time.
State of Health (SoH) tracks the history of the battery in the vehicle. Charge/discharge
cycles and times are monitored. SoH helps the DME determine the proper
charging rates and anticipated battery life. Internal resistance of the battery is calculated
by the IBS from the current and voltage dip during engine start. The values are
forwarded to the DME to calculate the SoH of the battery.
Software contained in the microprocessor of the IBS utilizes the measured values to calculate
the State of Charge (SoC) of the battery during vehicle sleep mode and compares
this information with that received from the DME/ECM pertaining to the battery SoC/SoH,
during the period of time between engine "OFF" and deactivation of the DME main relay.
The current SoC/battery data is stored in the IBS every 2 hours over a 6 hour time frame,
providing 3 - 2 hour snapshots of battery SoC information. The stored information/snapshot
data is overwritten every 6 hours. Whenever KL15 is activated the IBS updates the
DME with the current closed circuit histogram/battery status information, byway of the
BSD. Upon obtaining updated information the DME evaluates the new data and if a
closed-circuit current draw is identified a fault will be stored in the fault memory of the
Voltage (6 V to 16.5 V) Starting Current (0 A to 1000 A)
Current (200 A to +200 A) Temperature (-40C to 105C)
Closed Circuit Current (0 A to 10

Here is the reference that might help on other E90 systems

Last edited by fun2drive; 01-14-2013 at 10:00 AM.
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