Galaxy SII charging problem.

[Stancee]

Hello there!
So here is a weird (I'd say) problem with my phone:
I usually charge my phone at night, but this time something weird happened.
When I woke up two days ago I unlocked my phone to see what hour it was, and I saw the battery percentage at 3%.
I thought I didn't plug it in the proper way, and I tried to charge it with the usb cable (charger and usb are original).
I didn't have any problem with the usb for about three days, but last night it happened again. When I plugged my phone in, it had about 30% of battery, and when I woke up it was at 4%.
I wiped the battery stats, as I thought it was a bug or something, but that didn't change anything.
Can it be the battery, or something else?

 

[Titillating]

Possibly a loose/bent connector. My phone does something similar, only charges if it is plugged in in a certain position. Fairly cheap to get replaced, even if you bring it out to a professional.