Jim, the "+" is pressed/stamped into the top of the battery and clearly shows in the thumbnail picture you attached to Post #9. Any knowledgeable MB owner should know that the negative terminal is ground.

I guess your friend is one of those people who reads the Owner's Manual after suffering from a self-induced problem. My first instinct would be that using a booster would be OK if connected properly, but I would have checked the Owner's Manual before assuming anything.

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Fred Hoelzle