PS Vita 2000 slow charging

[BrazilianSniper]

I bought an used Japanese PS Vita 2000 about an year ago and is just so slow to charge.

 

To charge, I do use my North American OLED power brick with the usb cable that came with the system or I even use those usb chargers with multiple ports for various devices (that charges my OLED just fine btw) but on this 2000 model has similar results as using the power brick. The charging is basically all over the place as well, sometimes stays on charging for a day and get 50%, but next day the same amount of time would only get 30%.

 

Does anyone experienced this or know what the problem could be?