Had to get rid of my 640XL...it had severe battery drain for a windows phone(The sole reason for buying this phone was because of its battery life and camera..and I was not impressed)....I just used screen lock and unlock to check normal messages when i was at work...i was shocked that it lost 26 - 27% in 6 hours..and i hardly touched the phone once or maybe twice for 2 to 3 minutes each hour to reply back..The battery saver mode was always on and no back ground tasks running...Iam feeling down that my hard earned money was wasted..within 2 weeks of purchase...My gripe about this phone was that it took around 4 hours+ to charge and if it cannot even last a single day..then whats the use of the phone? luckily I got my 172.6$ back...and this is the last time ill try my luck with a windows phone..
P.S I still will never regret owning the Nokia Lumia 720...it was the king of all the Lumia devices till now..at least for me.
Wow, maybe your phone has some issues regarding the hardware. Have you try hard reset?Have you any friends who have the same phones to compare the battery life with?
My 640 XL is so good in battery that I'm so in love with it, of course for regular use in 2 days. If I put it on hard pressure, it can last for 1 and a half day.
For the charging issue, I think Microsoft has made a quite bad idea when supplying the 750mA adapter YET it can give us the so-called reasonable price. I think you can change into the 1.5A adapter from the lumia 1520 or from Sony, which takes you only 2 to 2.5 hours to fully charge the lumia 640 XL.
PS: I'm using the 1.5A Sony adapter now and everything turns fine now.