Already tried that buddy.. on the tail underside of the fuselage, there is about 150mm from the tip of the fuse back towards the front of the plane that is balsa/ply sheeting from there forward to the wing/fuse opening its open frame.. so on the section of balsa sheeting at the back there is already a hatch opening for the rudder servo.. so i cut the hatch further to the tai as far as it could before the tail wheel.. but after all that the battery was too thick to slide into the tapering tail.. so i had to redo that section.. i then looked towards just before the rudder servo hatch in the open frame section but the dual elevator servos are mounted there and i wasn't keen on mounting the battery on the servo's in case of interference for whatever reason. And any further forward than that and it may aswell be where it is at the back of the fuse/wing opening. So atm i can't think og any other way to set it up.. other than to just fit some slim lead pieces into the tail cos thats all that will fit.

P.s. Its a CMPro 65" Extra 300s.. the 90 2c/120 4c size plane.