mophie slowed charging times

[Nightmeare]

I just got a mophie for my gs3, and tried to treat it the same way I used to on my iPhone back when I had one. I kept trying to charge my phone with the mophie on and the battery would charge slower than it would deplete as I used my phone. I tried removing the mophie and it would charge fine and I am currently testing if the mophie alone will charge it, is there any way I can get the mophie on and have both the case and my phone charging? thanks