Notes For Cars With Twin-Battery System
Notes For Cars With Twin-Battery System
Safety instructions for handling vehicle battery.
Block diagram for twin-battery system
Components and their installation locations:
- 110 Ah starter battery, rear right
- 55 Ah system battery on a swing-out carrier above starter battery
- A safety battery terminal (SBK) on each of the B+ terminals
- An electronic disconnecting switch on the outside of the swing-out battery carrier
- Control unit, electric catalytic converter, under carpet of front right seat
- Additional B+ support point in engine compartment on left wheel arch
Operation of electronic disconnecting switch:
In starting sequence with system battery flat/faulty
When terminal 15 is detected, the voltage here of the system battery (55 Ah) must be >1.5 volts and the electronic disconnecting switch closes for 30 seconds. Electrical system is thereby supplied via starter battery (110 Ah). The starting sequence must now follow within this period of 30 seconds. Starting sequence can be repeated several times by detecting terminal 15 again. If system voltage is <1.5 volts: starting is no longer possible.
In starting sequence with starter battery flat/faulty
Engine starting is no longer possible if the starter battery is flat/faulty. The assistance of the system battery is not possible as the electronic disconnecting switch is only designed for a maximum current flow of 60 A and this is exceeded during the starting sequence.
Stationary operation/neutral position
In stationary operation/neutral position, the electronic disconnecting switch is in "Sleep mode". A closed-circuit current of >1 mA is essential for this. The electronic disconnecting switch is always open in stationary operation/neutral position. The closed-circuit current flows exclusively via the system battery (55 Ah). This prevents the starter battery (110 Ah) from discharging via the vehicle electrical system. The electronic disconnecting switch is activated either with detection of terminal 15 or at a battery voltage of >13.5 V (charging operation).
Driving/charging operation (alternator)
The alternator charges the starter and system batteries in parallel. The starter battery is disengaged if now the voltage of the starter battery is greater than the alternator voltage. Only the system battery is charged. If now in driving operation the system voltage drops below 9 V ± 0.5 V, the starter battery is cut in to support the electrical system. This can result in both batteries discharging.
Charging operation with battery charger
In the case of charging with a battery charger in the engine compartment, the starter battery is charged via the B+ support point at the front of the engine. In the case of charging with a battery charger, the system battery is charged at the rear B+ support point on the left wheel arch in the engine compartment.
NOTE: In the event of repairs or during diagnosis with terminal 15 activated, the battery charger must be connected to the rear B+ support point (engine compartment, wheel arch, left) in order to prevent the system battery from discharging.