brumey,
How is your set-up working out at higher speeds? Does the exposed part of plug-in attachment flap around at all? How distracting is it while driving (visually or/and any noise)? Is it visible from the driver's seat while driving (although I suppose you try to tuck it behind the hood...
Would it not be much easier to use a cigarette lighter outlet adapter (rather than OBD II port Adapter)?
https://www.batterytender.com/products/battery-tender%C2%AE-quick-disconnect-12v-outlet-adaptor-cable