so to your question for the 15000 pineapple batteries. - yes when all led's are steady lit they are fully charged.
for the connection use one y cable with the two usb's on one end and then micro usb connector. plug each of the usbs to the 5v 2a battery port of each pineapple batterie (2 of them) and the micro usb should then be connected to the uart port.
use your normal usb to micro usb cable from your phone for the tethering part. plug that one into your phone and to the usb port of the tetra. enjoy :)