I will just add that I'm quite surprised at the effect of opening a door (which triggers a bunch of computers to wake up) has on auxiliary battery resting voltage. I just measured over 12.7 V after a long rest, whereas it was just over 12.5 V just after I opened the doors (I foolishly left my multimeter in the glove box after yesterday's measurement before an errand). That makes a huge difference to the apparent state of charge!
Please ensure the following when you make this measurement: 1) ELM327 [OBDII dongle] is not plugged in. 2) You do not open any doors following the charging cycle. In other words, open the [bonnet] before you start charging so that you can measure the voltage without waking up the car electronics.
Edit: I meant to add that I guess the large difference in voltage after opening a door is due to a pulse of current temporarily wiping out at least part of the surface charge, and that surface charge appears to be able to re-form over a period of hours. Lead acid batteries are weird things.
Edit 2: that means there may have been considerable life left in the original battery, and I basically wasted $200 replacing it a year ago. Sigh.
Interesting, that's a bigger voltage drop that I thought. I wonder how much of the drop is because of the interior light. I would've thought the high current draw of a filament bulb would be more than a few computers. But I guess the computers could be fairly energy intensive depending on what they drive. Either turning the interior light to off, or replacing it with an LED (like I did) would confirm it. I just haven't done the measurements.
I used to have a Leaf 2012 and have the same problem with accessories battery very under charged. I was surprised to discover in the User Manual that for the accessories battery to be topped up automatically, you have to unplugged after a successful charge, this was not practical for overnight charging and morning warm up. What I did to overcome this problem was running a cable (with fuse and socket) from the battery to the charging area and trickle charge the battery with an external 12V charger from there, I only using it if the car is idle for a few days and plugged in.