Xperia E5 weird battery behavior

[LabregoPT]

Hello everyone!
So, I've been having some trouble with my device's battery lately. Battery drains in a (I guess) normal rate, but when I try to charge it it takes forever to charge. I'm conscious about the thing with AVG and my model, but I guess that's not the problem as I have had it disabled since months ago. Also, my battery doesn't charge or takes a really long time when charging, even if I charge it while turned off; and I've had weird cases in which my phone was in a percentage before turning off, and when I turn it back on it's in a different percentage (i.e, last night before turning it off, it was in 2%, but when I connected it the screen displayed it was on 37%; or a couple of days ago, where it was on 57% and after I did the same, it was on 38%). This happens the same while on secure mode, so I have no idea what does the problem is.
Any ideas on what's going on with my phone and how could I possibly fix it?
Thanks!