I would advise you to take the junior model without the choice of amps, it does not really do anything. You can simply charge with less current instead of automatic 6-7 amperes at the beginning, although this does not make much sense, because. when charging, the amperage will still go down. At the moment, the difference is ~ 420r per twist, even without choosing 6V for moto - not very much. In short, it is much more profitable to take model 15 (aka 150).