Date registered: Dec 2005
Vehicle: W211 E320 Bluetec R129 SL500 - $1300 car ........ Ford F350 6.7l
Location: Vegas MAN, Vegas
Mentioned: 10 Post(s)
Quoted: 1250 Post(s)
Problem is, that without disconnecting the cables there always will be small current flow.
MB likes to keep the customers in dark and not telling how the system works.
In older MB we had them sitting with alarms on for 5 weeks and they always started up after. That is pretty impressive, but low discharge is killing the battery in accelerated rate and should be avoided.
So my guess is, that the SBC battery is not powering anything on parked car till somebody triggers SBC system to start (like opening the door).
The alarm suppose is powered from the big battery and this is the one who theoretically should be charged.
Than again my experience is, that big batteries can "hold on their own" for long time, while small, motorcycle style batteries are lesser quality and require more maintenance.
Best of all would be connect both battery to battery maintainers. I wouldn't hesitate to connect them to the same maintainer, but that would require long extension cables.
Or just disconnect the clamps on both..