Being somewhat new to battery R/C, I am still trying different things as far as switch and charging port locations.
Having some delicate powered units I do not desire to remove them from the track for switching or charging purposes.
My favorite access is under the water fill lid on a tender. Push buttons on the angled face of a chamfered fuel tank, a discrete mini toggle just behind a brake shoe hanger. 2.5mm port tucked into the inside void of a fuel tank.
At this point none of my R/C units need to be lifted off the track for on/off or charging purposes.
All my steamers have charging jacks on the tenders under a removable coal load. Diesel charging jacks were installed wherever I could find a place, under a removable hatch, on the side or bottom of a fuel tank, or on the rear of the unit, like on a F3 or E7.
Here's where I have the jack and the on/off switch on my Weaver RS3:
Steamers stay on the layout, diesels are on a roll-around only because I don't have the space for them in the yard and run steam 95% of the time anyway. I have 1 diesel that has the jack on the bottom (MTH NW2) which I have to turn on it's side to charge. I hate it but until I figure out where else to put it....
I drew this "charging jack column" a while back but never did anything else with it. Put the cord on a spring loaded spool that you could pull out and plug into the jack, then when done charging disconnect and let it roll back onto the spool:
Inductive charging would be ideal I think, just like charging a cordless toothbrush only at 9.6 to 12.0 volts, depending on what battery is used.