Ok so I am going to get a hana modz dna 20 or 30 from FT. I dont understand fully two things. The batteries recharge via usb but are replaceable so do you just replace once they wear out over time not every charge. Second on FT you can get it with a built in li-po an 18650 or none. Does one or all of these get charged via usb and whats the best one. I hear a lot about suspect FT batts so if I can just put in an AW IMR?