The facebook app was chewing battery on mine, killed it a few times and fiddled with a few settings (but NFI what I actually did) and all seems fine again now. With fairly solid use it's rarely under 50% when I go to bed, if I'm home all day and it's on wifi then it only uses about 15% in 24 hours.
Cool story hey.
And yeah Barnz that's my understanding hence me suspecting it wasn't intended.