The link you found there is a link to the same instructions that are supplied with the unit.
The other instruction (I have just found out) have come from a dealer of these units who does not believe the original instructions are very good so has created his own. I am trying to get a electronic copy at the moment.
I believe Akku is a german abreviation for a battery, yes.

There is no seperate battery shown that is exactly my point, the original pdf set of instructions show units running without extra battery. and the polarity on these diagrams seem to show the positive from the center terminal of the plug.

Will have to get it plugged into a receiver and put a meter across the terminals and see what it produces