Jack,
I would follow Firedog advice.
make sure your second Eplus works - powers up normally, throttle works,
next
take second Eplus battery apart , remove control/process board and use it for your project.
for repair opinion I would have to see many pictures of damaged board from many angles and close ups pictures,
it requires high quality camera /in expensive $500-plus cellphone for example/ , cheap, shoddy camera will not show details.