We made a 'mock' battery out of a 1/4 inch styrofoam sheet.

The diagonal center piece is scotch-taped in to keep the rectangular form.

The we 'fit' the 'mock' battery into it's location at the front of the cabin. The bottom skin 'just fit' over the rear tubing. If we set the skin back with more overhang in the rear, the battery would not fit in the front.

Keep in mind that the fuselage is upside down at this time, as we are installing the bottom skin. Also, you have to play with the orientation of the 'battery'. It only fits in conveniently ONE WAY. If you turn it 90 degrees, you will pull the bottom skin too far forward.