This is a plug and socket design that is compatible with the Nissan Leaf 2011-2012 (Gen 1) traction battery B24 CAN/control plug and socket.
If you want try adding a secondary battery to the Nissan Leaf one approach is to create short extension cables for the main harness (both the high voltage DC cable and the companion B24 CAN bus/relay control plug and socket) then patch into those extension cables to run off the the secondary battery. This approach avoids the need to cut in to the cars wiring - which makes the whole progect non-invasive (you could remove the secondary battery and no harm was done to the actual car.
These 3D files allow you to make the B24 plug and socket yourself. Sourcing original version can be hard and/or expensive.
You'll also need:
* Male To Male Color Breadboard Cable Jumper Cable Dupont Wire (for the socket)
* 1.5mm Metal Female Spade Terminal for Nylon Multi-Pin Connector (for the plug)
* 1mm Thick DIY EVA Foam Sheet (for the plug washer/seal)
If you search your favourite online-random-stuff site for those titles you should find the items easily enough.
* the socket design does not yet have any mounting holes.
* 3D printing these will not produce a waterproof connector - I'll be wrapping them in plastic to improve water resistance