OK.. First things first. If you completely power the phone off (not Odin mode) and then plug it in, it should show the "Charging" screen with the battery in the middle. If that shows that it's not charging, it means your battery has gotten too low and will need to be replaced.
*Just* having a low battery, though, should *not* have rebooted you into Odin Mode, so that is definitely weird. Once you get the device charged back up, I would recommend a factory reset, just in case there is some app in there doing strange things that may or may not be intentionally fishy.
And then, right after I typed that, I thought of a caveat: it's possible for an app to set a "flag" so that the device should reboot into Recovery. It *might* also be possible to set a flag to reboot into Download (Odin) Mode as well. If that flag happened to be set for some reason, then your battery died and the device powered off, then turned itself back on once the battery was charged up enough, that set of circumstances *could* have resulted in what you described. But that still doesn't explain why your device would have the Download (Odin) Mode flag set in the first place.
09-13-2016 04:34 PM