As question posted and comments after... Let always keep the : mission in mind. Having and old pack for a motorglider is ok just to take off and then glide. Just to get rid of the tow-plane. But on the efficiency.. the power /kg is still at about in lab of 1/6 of what gas is. Yes you can said you are green with battery.. but not efficient at all. On the r/c front.. 16yrs ago i got big Axi motor. I can just put the motor on top of a potato bag and it fly.. But for a 2min it cost about 1500$ for the batt pack. To get the mission of : i can take off a potato bag.. check. Efficient .. no. Those Pipistrel is about 60k to swap the batt. All in all it cost less to swap the Rotax 912. But hey you on gas you fill and 10min your are back up. Electric.. stay on ground for the rest of the day charging. 380v are not available in America and 240 not really present at any airfield.