Samsung galaxy note 10.1 GT-N8010 is charging REALLY slow

I've got samsung galaxy note 10.1 (GT-N8010). A few days ago I wanted to charge it. After a hour or two I saw that it didn't charge at all, the battery percentage was almost stuck (or it even drops down slowly). It only charges when the device is switched off (but it still takes much more time than before...). I'm using the stock charger (2,5A; I've tried with other chargers, but still the same) and the stock cable. I haven't installed any apps that could drain battery. Also no red "X" on the battery icon when charging. I've got all the updates installed (I didn't get any in the last year or even more). I'm running android 4.1.2 (branded) without any root and mods.