...and other clickbaity titles.
The Gen1 Leaf is a good car - it really is. OK, the aesthetics are questionable and the life of the traction battery isn't great, but its comfortable, nippy, cheap to buy thanks to the aforesaid battery life, basically free to run, and reliable AF - ours hasn't seen the inside of a mechanic's workshop in the 8 years we've owned it (and that includes servicing, since there's nothing to service). If what you need is a cheap city runabout and you have access to a power point at home, you can't do better.
However there are aspects of the 12V electronics which were clearly handed off to an intern during the design process.
- The circuit which charges the 12V battery off the traction battery only uses a charge voltage of 12.5V, so it never charges the 12V battery to more than 50%
- It only charges the 12V battery while the traction battery is enabled for other purposes (i.e. driving or charging) - it can't enable it purely to charge the 12V. So the 12V will go flat from parasitic loads even if there's plenty of charge in the traction battery. And once it's below 10V or so it can't pull in the big-ass relay which enables the traction battery, so you can't self-recover from that state.
- It doesn't have an undervoltage lockout for parasitic loads, so it's perfectly capable of draining itself dead flat. In particular, if you leave it plugged into its portable charger for three or four days it will drain the 12V down to 2V or less, because the charger electronics are powered by the car and once it's completed charging it disables the traction battery but keeps sucking 12V into the charger electronics.
... and now, the latest one I just learned: If the 12V battery voltage is low, it impacts the measurement of the charge state of the traction battery, so the car lies to you about how much range it has left.
I've been worried for the last few months that the traction battery of our 2012 Leaf was starting to fall off the End of Life cliff. The battery health indicator was still sitting on 8 bars, but the range was turning to shit; the trip into our nearest major town and back, which used to be comfortably doable on one charge, had become a case of "turn the heater off, slow down on the way home, and hold your breath". I'd checked the obvious things like tyre pressure, alignment and brakes and they were all good. It was getting to the point where I was thinking it was time to sell the car - if it won't do that trip without a charge at the other end, there's no point in us having it.
However last week the dashboard threw a hissy fit when I tried to start the car - wouldn't start, a random selection of warning lights wouldn't go out and the range was showing as "---", which I've never seen before. A quick forum search later and I found that with the Leaf, as with most modern cars, if the electronics start doing weird shit the first place to look is battery voltage. And surprise surprise ours was down at 10.5V. A bit of experimenting later and no, it's not holding a charge: time for a new 12V battery.
So today I go into town to get a new one. Buy it, swap it out in the carpark, and lo and behold the state of charge of the traction battery rises instantly from 40% to 60%. Which is where I would have expected it to be a few months ago after getting into town. Drive home without taking energy conservation measures and yup - normal service has been resumed. The 12V must have been sagging for the last few months, far enough to impact traction battery monitoring but not far enough to stop the thing working. Go figure.
So that was a cheap fix 
Interestingly, although the range as measured by remaining charge level on the dashboard graph has improved substantially, the range predicted by the digital guessometer hasn't changed at all. Which confirms my impression that the guessometer doesn't use battery charge state - or any other actual "facts", for that matter - in its prediction algorithm.