Many devices have a regulator that goes into trickle charge as the device gets close to 100%. This is what you may be experiencing.
Mine goes from no charge to full charge in about 3 1/2 hours. The led does go to green. I get about to 90% charge in about 2 hours.
Now if I only slightly discharge it then it can take a while to go back to green but it does get there. Individual batteries, like people, can have their own quirks.