Intelligent battery sensor and battery


Brief component description

The following components are described:
  • Battery
  • Intelligent battery sensor


The vehicle battery is fitted in the centre at the rear of the luggage compartment floor. In BMW 7 Series or 5 Series GT an AGM battery (an AGM battery installed ex works has a black housing and no magic eye). The AGM battery has a capacity of 90 Ah. The AGM battery primarily offers the advantage of greater rechargeability.

IBS: Intelligent battery sensor

The IBS is a mechatronic, intelligent battery sensor with its own microcontroller. The microcontroller is an element of the electronics module. The electronics module records the voltage, the current flow and the temperature of the battery. The following components are fitted in the electronics module:

  • a precision resistor (resistor for current measurement)
  • a temperature sensor
  • evaluation electronics on a printed circuit board
Item Explanation
1 Negative battery terminal
2 Intelligent battery sensor
3 Battery earth lead

The IBS continuously measures the following values on the battery:

  • Terminal voltage
  • Charge current
  • Discharge current
  • Battery temperature

The IBS is connected with the engine control (DME or DDE) via a local interconnect network bus (LIN bus) for data transfer.

Item Explanation Item Explanation
1 Measurement of the battery voltage between the positive battery terminal and negative battery terminal 2 Temperature measurement of the battery (T)
3 Microcontroller (μC) in the intelligent battery sensor (IBS) 4 Digital Engine Electronics (DME) or Digital Diesel Electronics (DDE)
5 Current measurement (A) [indirect, via the proportionally voltage drop (V) at the precision resistor (shunt)] 6 Negative battery terminal
7 Positive battery terminal  
LIN bus Local interconnect network bus (LIN bus) for transmission of the values to the DME or DDE

System functions

The following system function of the power management with IBS ("Advanced Power Management") is described:
  • Determining the battery's charge state

Battery state of charge

The APM with the intelligent battery sensor determines the state of charge during driving and when the vehicle is at a standstill on the basis of measured data:

  • Driving:

    • Balancing the charge and discharge current of the battery.
    • Calculation of the current characteristics on engine start to ascertain the battery condition.

    While driving, the IBS transfers the data across the LIN bus to the engine control unit (DME or DDE). The software in the IBS controls the communication with the higher-level engine control unit (DME or DDE).

  • Vehicle standstill

    When the vehicle is at a standstill, the measured values (open-circuit voltage measurement) are queried in cycles to detect energy losses. The measured values are entered in the IBS in the memory and transferred to the engine control after restarting the engine.

In the engine control, the following data is saved along with the battery's charge state history:

  • Battery state of charge of the last 5 days.
  • Charge status histogram showing periods in the ranges 0 - 20 %, 20 - 40 %, 40 - 60 %, 60 - 80 % and 80 - 100 %. The charge status histogram is reset in the following cases: engine control (DME or DDE) programming or battery exchange registration.

Notice! Evaluation of the battery state of charge!

If the rest phase is not sufficiently long or if there is a standby current violation, the state of charge cannot be determined correctly: the state of charge is implausible.

Startability limit

The Advanced Power Management (APM) calculates a lower and an upper startability limit for the battery:

  • The lower startability limit corresponds to the minimum charge state of the battery so that the vehicle can still be started.
  • To counteract discharge down to the bottom startability limit, a certain charge volume is kept as a reserve. To achieve this, the upper startability limit is calculated. This value is used e.g. as the limit value for the requests for deactivation of terminal 30B when auxiliary consumers are active.

The startability limit is calculated by evaluating the following measured variables:

  • Average battery temperature with vehicle parked.
  • Ambient temperature of the last journey.
  • Current state of charge.
  • Voltage dip of the last engine start (trend for ageing of the battery).

Notes for Service department

General notes

The following general information is provided:

  • Assessment of the battery condition.
  • Charging and trickle charging of the battery.
  • Replacing the intelligent battery sensor (IBS).

Notice! Assessment of the battery condition!

The battery's condition cannot be determined based on the battery's state of charge alone. All batteries are subject to natural wear due to the natural ageing process. The chemical reactions in the battery, consisting of the charging cycles with battery charging and discharging, mean that deposits form in the battery, preventing the battery from reaching full capacity.

Item Explanation Item Explanation
1 Charge battery. 2 Discharge battery.
3 Ageing / deposits 4 Self-discharging.

Each total discharge results in a loss of battery capacity: The longer the battery remains completely discharged, the greater the loss of battery capacity. At the same time, the batteries installed at BMW can withstand multiple brief total discharges or as many as two long total discharges, provided that they are subsequently recharged at a constant charging voltage of 14.8 V.

If a battery's charge is low, recharge it before returning the vehicle to the customer.

Notice! Charging and trickle charging of the battery!

The battery may only be recharged with a battery charger that has been approved by BMW and that has a constant charging voltage of 14.8V. If possible, the battery temperature should be between 15 °C and 25 °C during charging. Under these preconditions, the battery is adequately charged when the charge current drops below 2.5 amps. If the charging procedure is carried out at low temperatures, it should not be ended until the charge current drops below 1.5 A. If the battery is to be charged while it is still installed, it must be charges using the jump start terminal points. Only then can you be sure that charging is correctly recognised by the vehicle electronics on vehicles with an intelligent battery sensor (IBS). If the battery is charged directly at the battery terminals, this could lead to a misinterpretation of the battery condition and even unwanted Check Control messages or fault entries. The cigarette lighter gets his voltage supply by the front power distribution box via the switched terminal 30B. After terminal 30B off, the relay de-energises. This means that a trickle charger connected at the cigarette lighter would be disconnected from the battery. Only charge the battery via the jump start terminal point. When vehicles are in long-term storage, or remain parked and stationary for extended periods, their batteries should be recharged at the regular periodic intervals prescribed by the Battery recharging schedule.

Notice! Replacement of the IBS!

The vehicle must remain in a passive state for at least 3 hours after the new IBS is installed: Only then can the new IBS determine the battery condition. The Check Control message "Extreme battery discharge" no longer appears when the battery has an adeqauate charge, and the battery's actual state of charge can be displayed.

Diagnosis instructions

Notice! Register battery replacement!

After installing a new battery, the service function 'Register battery replacement' should be run. The battery exchange has to be registered in order to inform the power management system that a new battery has been installed in the vehicle. If the battery replacement is not registered, the power management will not function properly, with the result that Check Control messages may be displayed and functions limited by individual electrical consumers being switched off or having their power consumption reduced, for example.


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