Ok I found the answer from youtube's Dronado FPV. I bought this from amazon, should connect to my imax b6.
The one he recommended is called Crazepony 1S Lipo Battery Charging Board. Hope that helps other people that has the same issue. I would love to find an ac adapter too, but apparently...
I have one of these with a wall plug and a regular charger plug in, and a usb out. What do i connect to the wall plug side to charge this thing?
Its one of these
https://www.eachine.com/Eachine-QX65-E010-E011-E013-6-In-1-3_7V-1S-Lipo-LiHv-Battery-Charger-Board-p-1151.html