[Linderpat]

It is not an issue to disconnect the battery as you do. Modern cars are more suseptable to this with the advanced computer systems in them. The 928 was pretty simple in this regard over its run. It is, however, a pain in the rear to access the battery and disconnect it. Instead, a battery tender is the best option. Get any decent one at your local parts store. The Battery Tender is a good option. You most definitely do not need a Porsche branded unit. Use the front jump post for the (+) and the bolt on the cross member for the (-) clamps. Alternatively, a lot of guys do use a quick disconnect to "unplug" the car. Honestly, driving once per week, you should never have to worry about the battery draining without doing anything, unless something else is wrong, causing a parasitic drain.