I'm seriously considering this battery in my kitfox. I currently have the pc680. My question is: there is the ETX680 and the ETX680c, they claim that there is only a size difference but I want to know from people that have bought this battery what they would buy. I want the best of course. I also want to know if the charger is really needed. I fly a lot, at least 3 times a week. I have the 912uls in my model 4. thanks