It hasn't been near water I had the same thing with another phone that i'd use as a bathroom speaker occasionally, I learned from that experience..

The Phone does act the same as it would do when the battery runs out but the battery is full, I ordered a new one hoping it might fix the issue, I would reflash but it says not to attempt it when you don't really know what you're doing (I have minor Ubuntu command experience, but it's not really enough and this is my only phone in my possession I would actually like to use, so yeah).