Roundel magazine, February 2011, page 99:
... One of the computers actually tailors how the alternator charges the battery; it takes into consideration both the type and age of battery, so it needs to know when you replace the battery so that it can determine how to charge it. It doesn't charge a fresh battery the same way it charges an older battery, and there's a good chance that the computer will charge a cold battery too aggressively, or over-charge an AGM-style battery, which needs to be charged differently from a conventional battery. Ignoring this registration won't necessarily trigger a fault light, but there's a good chance it will shorten the life of the new battery.
Unfortunately, it takes a scan tool... Bottom line: Anyone can change the battery, but it will take someone with this special tool to do the job correctly.