I don't really care about the "time" said by the apps. I use Insider. I tested it. it was saying "1 day and 5 hours remaining" but I really used more than 2 days. Actually it was saying "1 day and 5 hours remaining" for about 10 hours and not a minute changed during this time !
I can get about 2 days with normal use and a whole day in the most heavy usage. I don't mean full-time gaming of heavy usage.
WiFi on, BT off, Location on, sending message, recording sound, Cellular off, making calls, and casual gaming about one hour and I get one day battery life on my L1520.