In order to keep my battery from going dead when my 2008 528i is parked for a month or two, I was in the habit of connecting a flow charger. This was really a nuisance since I don't have a garage.

So, I obtained a BMW cut out switch which was manufactured by Hella and evidently, installed in BMW's at the factory before they were shipped to the US and then removed upon delivery of the vehicle. I thought it would be a really cool idea to connect this cable and when I wasn't using the car, to just shut the battery off. I would only lose the clock, date, MPG's recording and radio settings. Evidently the seat and mirror memories are "hard memory" which wouldn't be lost.

So, two questions. First, what would be a good installation rather than just coiling it up in the trunk? And, second, do you think there would be a voltage drop over the total 18' of cable which would confuse the intelligent battery sensor system? Of course, I could possibly shorten the cables. Is there an issue with constantly running the electrical system through the kill switch? It is rated at 100 amps.

I attached a photo of the cable.

 

Not a suggestion to my post!

I'm surprised that there seem to be very few mechanically inclined owners in this forum. Volvo and Jeep guys (both of which I have owned,repaired and modified) would always have helpful answers.

 

There are plenty of experienced people on this forum that could help with thoughts/comments/experiences. It's just that these cars are so loaded with sophisticated electronics that many people back off from any primary electrical mods for fear of frying some (expensive) module or other. You are not alone. Another poster wanted to install an AC inverter. No one wanted to touch that one either. It just adds another failure point in your electrical system. If it is for two months or so, as you say, remove the battery, float charge it in your bathtub.

 

Personally I was told by the experienced BMW mechanic to do not disconnect battery if not absolutely necessary.