the batter started to drain really fast started beginning of last year and turn out not able to charge at all. And no way to fix it. So I stop using it and put it away in my cable cupboard, which is always dry and cool. Today happened I took out the phone again and found the back is bulged open, i think it must be the battery inside. You can't open the phone so I m kinda scared it might exploded. I don't even know where to store it.
Hi @Mika345, very sorry to hear about this. 
Since the phone is already powered off, please keep it powered off and get in touch with your Local support team as soon as possible and they will assist you further with having the device examined at an authorized service centre.
I hope that helps and let me know how it went!
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