sadly this doesn't work! I tried a couple of 9v chargers i had and i know with tech of this size im best not opening it.. it does have some signs of use. problems i have observed:
the top doesn't flip open but has to be lifted, not sure if this is typical,
the small arm which looks to have been attached to the lid is not,
the lid doesn't quite sit flush when closed, possibly due to above being out of position.
hopefully someone can fix it, including the original battery again I don't know if this still works.