What kind of battery needs to be at or charge at 14.8 volts? I assume you have flooded lead acid (FLA), not AGM or LiFePo4.
"The 12v battery charger is always on, attempting to get the battery to 14.4v . It is charging the 12V despite the 12V being at 14.3v disconnected from the car, which is rather high charge level. Normally 13.6 - 13.8 is 100% charged."
You are right 13.6v is 100% too much for fully charged... . Nominal voltage for a "12V" is 6 cells at 2.15v to 2.35v (2.2v nominal)*. So 100% SOC nominal on most FLA is 12.6v to 12.7v fully charged. But that 12.6v drops a 1/10th or two fairly quickly as you lose "surface charge". So if your battery is at 13.8v sitting there, that is a lot. (Please, let's not talk deep cycle, I am talking about generic car FLA batteries, not AGM which needs min 14.2v min and 14.5 or more to fully charge. LiFePo4 is another matter with on-board BMS.)
Cars use to charge at 13.8v constantly. You need something more than battery nominal cell charge to push the charge and overcome internal resistance. How much more is a big topic and varies with temp and battery type. 13.8v was a good compromise, but as cars got more electronics the voltage regulators in alternators set higher voltages..... Now cars push 14.2-14.7v and the most I would push FLA charging, more than that is cooking off electrolyte. If you have been charging at higher voltage for long periods you may have cooked battery low on electrolyte. (Cars with dumb constant high charging voltage is responsible for early battery death in MHO. Later alternators, say 20 yrs ago or more, got micro processors which helped a little. My VW bus voltage varies and drops bus voltage down, after battery is charged. Not a fan of "maintenance free" batteries you can't check electrolyte. The maintenance free part is they die in a few years and you buy a new one. No maintenance just money.)
To understand your battery is not being drained but being overcharged? Your comment about timers, charge, climate I assume is a 2012 LEAF thing. Not sure how that would change anything regarding battery charging, battery use but not charging. The drive battery to 12v charger, is software driven I assume and don't now what and why it does what it does. I can tell you my 2015 I bought used end of 2017, had dreaded OEM battery drain issue. Manually charge it. Fine for a bit, than dead. Battery tested OK. Bought new Walmart battery (5 yr warranty). Now 6 yrs later not once have I had a drained 12v and battery is still going strong. I did buy smart trickle charger and if car is not used I will charge battery on rare occasion. This leads me to your issue.
My wild guess. The battery is bad? Did you check it with a battery tester? Old school observation, is holding charge, is it starting car (gas engine starter). Since we don't need to load the battery with high drain starting, old school carbon pile load tester could be used. I assume you need this for transportation, but I would disconnect the 12v battery and test it and see if it holds charge, charge it with a good charger, see if hold charges and last load test it (old school carbon pile, or new school, solid state tetster).
NEW SCHOOL and most common now for battery testers for the DYI'er are solid state units that measures internal resistance vs. type and capacity. Just for grins go to Amazon search battery tester car, you will see a lot of testers from $40 to $260. Or you can go to AUTO ZONE or Advanced and ask the counter guy to get his tester out. When he asks you to start car just decline.
If you have clamp on DC AMP meter try that. I can't believe the battery is accepting a full Amp plus when fully charged. Chargers, at least smart ones, go to trickle when battery is fully charged. Trickle charge is on the level of milliamps (mA) not amps. Again my guess battery could be bad. Don't know, but need to eliminate that.
Question, how is Leaf Spy Pro telling you battery is charging? I have not used my Leaf Spy Pro for 10 months, and before that may be 10 times over 6 years. I never noticed this metric. I use mine mostly for drive battery SOC/Capacity/Battery metrics, codes, setting preferences, tire pressure.
