Battery life on the Amazon Fire Phone has been impressive. It has a 2,400 mAh battery in it, and given the specs on this phone, that easily lasts through an entire day - sometimes it even goes a day and a half.
Thanks to a 720p display and software that isn't so power hungry, you really won't have to worry about this thing dying on you at the end of the day if you've unplugged in the morning.
Almost not surprisingly, along with good battery life, the Fire Phone has pretty good performance, too. Of course, the software seems really bare bones, and again the display resolution isn't as high as what you'd find on most flagship phones today.
During my long period of review, I can't recall a single instance when an app stalled or crashed. That's impressive for any smartphone. And with gimmicks like Firefly and Dynamic Perspective, it's even more impressive.
The downside is that many of those apps don't get updated in a timely manner, or there are strange update features that you can't take care of because of the ecosystem. What I mean by that is these are Android apps that will occasionally give you a pop-up or in-app notification telling you an update is available. However, you can't update because you don't have access to the Google Play Store.
Still, this hardly affects performance, but you will have to wait until those issues get sorted.
When opening up the camera, swiping around and performing other actions, the Fire Phone doesn't ever slow down. There wasn't a single time when the phone suffered from a hiccup or lag.
For a midrange phone, I'd say this is rather impressive. Again, you're paying for it with scant features, lower resolution and a lack of customization options.
As far as call quality goes, remember this is exclusive to O2. It performs well in terms of O2 coverage, but make sure you're not already in a blackspot as this phone isn't going to help a lot in those situations.