I do my own battery changes but i should qualify that statement saying I am a dive professional certified as a tech.
That said and having read other replies I also want to state:
Warranties do not end because a user replaces their own battery on computers that have batteries that are by design and manufacturers intent user replaceable. Flooded devices do occur and that is usually because the user did not properly inspect, replace and or lube O-rings. Yes, under warrant you avoid that issue by having a authorized dealer replace the battery. Once the warranty on a computer is over even having a shop replace a battery isn't going to extent a warranty on anything but the battery. It may get you a credit or discount on your next computer.