Bob, instead of a recoil have you considered a long descending loop of wire much like that along the side of some elevator shafts? A recoil may work harden the wire after repeated use.
There are fine stranded wires like those for vehicle door / window control power but I always look for a kiss approach.
I used that principle in my antiquated lift up panel with drawer style circuit boards. The panel wire bundles go through the mounting board of the MTH blocks then come back up after a 12 inch "U".
I am thinking this just may help get past the recoil development and go right into a charging application.
Your water spout is a great idea. Also applicable to diesel oil fill. I am using the diesel tank for a charging jack mount already so that is perfect.
Bob Buck drilled out my tank for both a switch button and a charging jack. He was able to squeeze a Pico R/C battery system into a twin tower drive P&D platform geep.