I updated my Lumia 640 from WP 8.1 to WM10 .164 through upgrade advisor app and also hard reset the phone, but I have been experiencing massive battery drains. I find it hard to even get a day's usage while earlier it used to get 1.5 days on a single charge. I also updated to version .218 and again did the hard reset but nothing helps. Is this the general problem windows 10 mobile? Battery is very important aspect for me as most of the times I travel and don't get a charging point. Any help would be appreciated