Crashing, turn off and massive battery loss

So a few times now my note 4 has crashed (black screen) and turned off. When I turn back on the battery level has massively dropped (30-40% gone) yesterday went from about 40% to 0%. The 40% seemed accurate as using it not too much and usually about that percent at that time of day. Also noticed a few other things, when I connect my note to the pc it takes a while to start and stop charging and isn't being recognised by the pc (or the note isn't detecting it is connected to a pc - only charges)

Any ideas?

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