Whoopsy:
Carlos from Spain:

The problem is that the batteries cnnot be replaced, they are "fused" to the sensor's themselves so when the batteries run out, you have to replace al four sensors. But I replaced mine and they charged me somewhere around 500-600€ I think.

 

Wow, you got robbed. My 4 news extra ones cost like $90 a pop, and we already get shafted by Porsche pricing.

Carlos may be talking about installed pricing.  I think four sensors at $90 each uninstalled sounds about right.