Battery Full [Q] battery gone from 72% to 5% in 30sec -lagging-

Hey everyone
I got little problem here
So here is the situation it had happen 3 times this weak to me
When am using my phone (RR3 or facebook...) it freeze or lagged sometime,
That is natural to happen sometime
But in those 10 days when it lag it freeze for 30 sec/ 1 min
Then it restarts, but when itís restarted the battery is gone, from 72% to 5% in, how is that possible ???? (pic 1)

And if I donít put it in charge immediately it will just turn off after minutes!
_Still when I put it in charge and after like 20 min in charge I noticed that had already reached 80% just like if it had not started charging from 5% but from 60% !!! (pic 2)
_And sometime without any freeze or lag, it just turn off after showing that the battery is low 20%

So what is that?? A system / Hardware / or battery life problem??
I have this phone GS2 from 3 year now, and Iím using it like a geek
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