Just downloading that app...
When I first upgraded my 640 from 8.1 to 10 it was diabolical. Over the past few months I've spent some time optimising settings and also, I guess, getting some updates and now it's pretty good. Had three full days without a recharge, 2 half-hour stints listening to music on my bike, only one call, fair bit of browsing/whatsapp etc. I have email, IMDB and Kindle installed, which have all downloaded stuff etc. Always hard to compare I know, as everyone's usage is different.