Why not stick with the standard SAE 2-pin plug as used by most every battery charger/conditioner? I add a bulkhead surface mount version to every aircraft in an easily accessible area, usually externally. On an RV-8 I like one inside the forward baggage area on the aft side of the firewall. On tube and fabric aircraft I like to install one on a belly fabric inspection panel. These bulkhead versions have a tethered protective cap to protect from weather.
Sticking with the standard there are no special home-brew plugs interfaces. Works with any charger with the standard plug pigtail. Plenty good for avionics power as referenced in original post. Compatible with everyone's charger home or on the road.
When camping with my Husky I can attach a solar charger or use the socket plug to run an air mattress pump or charge a cell phone.