Changing car battery on an audi?

i heard rumors about changing the car battery on the audi resets the deck and it wont turn on unless you have a code for it. i bought my audi used and it didnt come with any of that. is this fact or a myth because im thinking of changing my battery out for an optima. also how difficult is it to change the deck to an after market deck. i also heard rumors that if you do it can mess up your cars electrical and on audi%26#039;s it takes a long time to get the wiring together. can someone please explain and filter whats a myth and what is fact|||Go to a large garage most of them will keep your Electrics alive as battery replaced.A code saver is connect before old battery disconnection.|||It is a fact you%26#039;ll need to re-enter your stereo code, you can have it looked up through the VIN through any local dealer. Or you could use it as an excuse upgrade the whole head unit with something nicer.