If your phone is rebooting itself randomly, my advice is attempt a hard/software reset and do NOT restore it from backup. Failing that, it's possibly a hardware defect and should be replaced. At least one person I know had this issue and is replacing hers.
All of the other issues I've seen listed are a combination of known bugs in the W10M build installed on these (10586.0) versus latest Insider Preview-- 10586.11. So hopefully that's good news for most of us coping with those bugs, and this includes the battery life issues. EDIT: I had crappy battery life on my 640 with 10581 Preview build and 10586.11 was great with battery, so I'll expect that we see this build or newer in very near future.
Also, if you are experiencing severe battery drain, my advice is disable Windows Hello for now. Also regarding Windows Hello, I'd love to have audible instructions for those of us who wear glasses and are blind as bats (yeah, I'm 20/2000 vision so I count in that), but calling it "unusable" just makes you sound snobby. Relax... just lower the glasses on your nose enough to look over it and watch the green bar. If it turns yellow, move closer or further from the phone.