You have to apply binary search on the answer (maximum possible amount of energy that can remain in each of accumulators after the transfers of energy).

Assume you have a function check(x), which returns true if it is possible to transfer energy in a way that each accumulator has at least x amount of energy at the end. It is trivial that if check(x) is true, check(y) for y < x is also true. Now binary search can give you the maximum amount of energy that can remain in each of accumulators by calling check() function.