Electrical System Charge Retention Unit For Battery

Overview Of Charge Retention Unit:

The charge retention unit is an MB accessory part which prevents the battery discharging due to quiescent current consumers when the vehicle is laid up for long periods.

The charge retention unit can remain connected to the vehicle for months without any problems.

Any grounding-type receptacle supplied via a 220 V or 110 V mains can be used as a voltage source for the charge retention unit.


NOTE: When the charge retention unit is connected the vehicle must be locked for insurance purposes.


A charging socket (1) for fixed installation in the vehicle and an adapter cable (4) with two terminal clips for individual use on other vehicles as well is included in the scope of supply of the charge retention unit.


NOTE: Adapter cable (4) is not included in the 110 V scope of supply (USA).


Fixed installation of charging socket in model 202 up to approx. 11/94
On the positive side (cable color red/green) the charging socket is connected to the screwed contact E, terminal 30 of the fuse box in trunk (F4).

On the ground side (cable color brown) the charging socket is connected to ground (right tail lamp in trunk) (W7/1).

Fixed installation of charging socket in model 202 as of approx. 12/94
On the positive side the charging socket is connected to fuse block A of the fuse box in trunk (F4). The positive cable (cable color red/grey) can be connected to receptacle C of fuses 1 to 6, terminal 30.

On the ground side (cable color, brown) the charging socket is connected to ground (right taillamp in trunk) (W7/1).

Fixed installation of charging socket in model 129
On the positive side (cable color, red/grey) the charging socket is connected to fuse 5, terminal 30 of the fuse box (F4) and on the ground side (cable color, brown) to ground (right wheelhousing in trunk (W7).