Default [Q] Charging rate decreases?

Hi guys,

So I'm having trouble with maximizing my charging speed (1900 mAh it was).
Using chargers other than the official S4's I would go down to about 500 mAh in a couple weeks.
Using the official S4 charger though, I also see decreased charging speeds.
My S4 has already went to Samsung for a repair on the charging hub, but I'm wondering if it is broken again.

Please any help/tips?