Definitely can cause a problem. last year my Merc C230k's battery kept running flat. Eventually Merc diagnosed it as a problem with the Netstar battery and CHARGED me for the labour notwithstanding motorplan, saying it was an aftermarket accessory (even though they approve the Netstar device
).
Anyway turns out the Netstar backup battery was flat/faulty and i had to replace it at the Netstar agent at my expense. System was only 2 years old.
Frankly, I think Netstar stucks. They take your car to pieces to install it and it requires major wiring and backup batteries.
This year I had a Cartrack installed into my 330i and the whole device is the size of a pack of cigarettes with minimal wiring, etc.
Hope that helps.