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Notes for disconnecting and connecting battery

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Observe safety informations for handling vehicle battery.

Before disconnecting battery:

Turn off the ignition and other electrical loads/consumers to prevent sparking when reconnecting.


If the ignition is not turned off when the battery is disconnected, fault memories may be set in some control units.


  • There is a danger of mixing up battery cables: If the battery positive and battery earth leads are the same colour and you are in doubt, follow the polarity to the battery, then mark and cover the leads.
  • On vehicles with radio code: After disconnecting the battery, the radio code must be re-entered. Therefore obtain the radio code card from the customer beforehand. Note stored stations and restore them after connecting the battery.
  • Stored settings of the on-board computer and clock will also be lost.
  • All available ignition keys with infrared transmitter must be recoded for vehicles with first generation infrared central locking.

General notes on disconnecting battery:

  • Do not disconnect battery leads and leads from alternator and starter motor while engine is running.
  • On vehicles with IBS at negative battery terminal:Do not under any circumstances pull/lever off pole shoes by force.

    Do not under any circumstances release the hexagon socket screw of the IBS.

  • Detach the terminal of the battery earth lead from the vehicle battery and the auxiliary battery if available. Cover battery negative terminal(s) and secure.
  • When work is carried out on the electrical system, faults may be caused in the fault memories of some control units when the battery is connected.
  • When installing battery terminal: Tightening torque 61 21 1AZ:
Type Thread Tightening specification Torque
1AZ Battery positive lead, battery negative lead, safety battery terminal, IBS

(screw connection from above)

E89 M6 5 Nm
2AZ Battery positive lid to distributor, safety battery terminal
E89 M8 15 Nm
4AZ Battery positive lead to transfer point
E89 M8 15 Nm

After connecting battery:


The scope of application of some systems may be restricted after an open circuit.

Likewise, individual settings may be lost.

Settings or activations must be carried out, depending on the equipment specification.

For example:

  • Vehicles with automatic engine start‐stop function (MSA):MSA function is active only after learning period (vehicle must not be woken for a period of approx. 6 hours) > if necessary, notify customer of the situation
  • E46 Perform (four-wheel drive) / E53 / E83: steering angle sensor adjustment
  • If necessary, activate slide/tilt sunroof
  • If necessary, activate power windows
  • If necessary, activate mirror with compass
  • Only E60, E61, E63, E64, E70, E71, E90, E91, E92, E93: mount steering angle

Please refer to the Progman user documentation for further information on vehicle-specific activation.

Vehicles with a two‐battery system

Starter and system battery

A circuit for the starter battery and a circuit for the system battery are part of a two-battery system. An auxiliary control unit monitors both circuits. Depending on the situation, the circuits are connected to or isolated from the auxiliary control unit via a cut-off relay.

Two AGM batteries, whose design and properties are described in AGM batteries, are used as a storage battery.


These batteries must not under any circumstances be charged with a voltage in excess of 14.8 V. Rapid programs must not be used either.

Receiving/giving starting aid via jump start terminal point

The engine can be jump-started with an external voltage supply via the jump start terminal on the right side of the engine compartment.


The starter battery is isolated from the alternators when the bonnet is open.

Giving starting aid via the jump start terminal point is thus limited by the capacity of the starter battery when bonnet is open.

Charging starter and system batteries via jump start terminal point

The starter battery is charged as a matter of priority with a charger connected to the jump start terminal. The voltage at the starter battery is the decisive factor in determining whether the system battery is also included in the charging procedure. The auxiliary control unit automatically detects a charging procedure at a charging voltage at the starter battery of ≥ 13.5 V. The cut-off relay is closed and thus the system battery is connected in parallel. Both batteries are now charged.


  • Terminal 61 inactive
  • Terminal 15 inactive

If terminal 15 becomes ”active” during the charging procedure, the cut-off relay is opened immediately and again only the starter battery is charged.


When the bonnet is open, the cut-off relay is also opened in normal operation when the engine is running.

A special mode can be set by means of diagnosis for workshop/garage operation. The cut-off relay is closed from terminal R in this operating mode. This mode is automatically reset once a distance of 5 km has been driven.

Trickle charging

The increased standby current consumption can be compensated for via the jump start terminal point with the aid of the ”Acctiva easy” battery trickle charger (Service Information 2 03 05 205).


The cigarette lighter is isolated from the electrical system after terminal R ”OFF” on a timed basis (60 mins.), thereby interrupting charging of the system battery via the cigarette lighter. This is prevented if the battery switch (on the right side of the luggage compartment behind the panel) is turned on and off again twice within 2 seconds.

This post was last modified on April 7, 2018 2:56 pm

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