Yes, own idea after looking for a connector inside that remains live when ignition is switched off. There was a nice commercial lead with in-line fuse, but I cannot find it now, lots of others that might or might not be suitable.
OBD2 socket power only has a 10A fuse which feeds other essential stuff, so it is NOT suitable for a beefy battery charger, but a weedy Solar might be useful at putting off the evil day when a proper charger is applied under the bonnet.
Here is a previous post of what I tried in April with OBD2 pinout picture
and then in May
The borrowed charger was later and in the summer, but very disappointing so not worthy of a post.