Like others said it should not be any different than another maintenance free battery. You should get a maintenace free sealed battery as it sits inside the car and not "outside" in the engine compartment. I would take out the existing one and make sure I get one of same dimensions (so it fits) and having the poles in the same place (otherwise the cables may not fit, but you need to check). If it is off a little bit in capacity I would not bother. Should not cost more than 100 Euros I would think, but that is a guess.