Phone was at about 10% when it died while recording a video. To my surprise it instantly started to turn back on, but it blacked out before finishing boot. Since then it is in a constant loop of booting and dying. I tried draining the battery first and then charging it overnight, but as soon as it had any power it resumed the boot loop. The phone is not visible in iTunes. I tried various button hold combinations, but none seemed to have any impact on the phone. This is a first gen SE, bought soon after the original release. Since then (March 2016) I've replaced the battery twice. I understand this is not an optimal use case for the iOS beta, and by no means do I expect Apple to fix the phone for me, but be warned: yesterday I've had a working phone and now it's as useful as a brick. I'll now attempt to wait for the battery to drain completely and then I'll see if iTunes will be able to detect it before it resumes the bootloop.