A beefy battery
Samsung has stuffed a 4,500-mAh battery inside the S20 FE, which is 500 mAh more than the battery it put in the regular S20. It's no surprise that it has a lot of power to offer. I haven't yet been able to do our full suite of battery-drain tests on the phone, but after an hour of YouTube streaming at full brightness, the phone had only dropped by 7%, which is very good.
Anecdotally, I found that it had well over half its battery left after a day of photographing, playing videos and doing bits of gaming. I have no doubt that it'll comfortably get you through a full day of mixed use and probably well into the next. It also supports wireless charging as well as 25-watt fast charging to give it a quick juice up if you're about to head out.