Is the battery not just the same as the micro filter, not traditionally part of an oil service but necessary due to progress. I open the vents on my old land rover I get flies in my teeth! And the key and lock thing when it's raining is a ball ache specially with a 50 year old key.
My batteries are covered by the service pack but if they weren't I wouldn't mind them doing it every service or 2 years and if I've changed it recently and forgot to tell them so be it, there not psychic and I'm not getting the damn bing and getting stuck in the rain. I know £9 for a £3 battery is a big markup but then so is a genuine filter made by Mann etc.
£9 every 2 years is 1.23 pence a day and seeing as it rains everyday in the uk I have had worse value for money.
Thinking about it when the crappy weak plastic tangs break on the battery cover if they break them surely the key wouldn't be returned with stick tape holding its guts in as they damaged it?