long-term charging the two batteries of 750i simultaneously
for this job I can only guess two possibilities, I have not done this already:
1) ask BMWs inside technicians, who can assure, that charging at the starting poles in the engine compartment will charge both batteries at the same time (I'm not sure if this works !).
2) if 1) cannot be answered definitely, do this by yourself-technique:
a) take the CTEK charger
b) connect minus to chassis Ground
c) split-off its plus-output by two resistors of 2.2Ohm/5W (cement type),
- connect one resistor "output" to the plus of the start pole in the engine
compartment, which charges the large starter batterie
- connect the second resistor "output" to the plus of the cigarette lighter
which charges the smaller bord batterie
d) limit the voltage output of the CTEK to about 13.2 V
e) if you apply this method, one should be shure, that both batteries may be held at e.g. 13.2 V for your long "winter sleeping time", without gasing effects.
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