Welcome to VT Michelle,
Did you try the Clean Cig carts on the NJoy batts? They appear to be RN4081 batts but I cant tell exactly from the pics on their site. As to the question "how long does liquid last?" it will vary from vaper to vaper. If you vape a lot its not going to last as long. I go through 5-7 ml of juice a week, some do that in one day.