I find the Z2 is quite tempermental and if not kept entirely happy then it has a tantrum, shuts itself down and won't power on again for a while. I have found that if it gets too hot then this will happen but it's happened other times too. It seems to recover itself within half an hour or so and then will turn on ok. Strange!! This device has many 'little ways'!!!
I guess you're right about it being tempermental. I guess I left it too long for charging, the reason for the heat causing it to malfunction. I have spared it this week, and noticed it behaves normally now.
I actually love everything about it. The size & micro-sd option is my main reason why I keep it. The only problem is some files recognize the artwork while others dont.
JetAudio maybe needs to do an update for the overcharging issue (if there is any)