If you put a voltmeter on the battery every time you push the start button and ever time you charge, the voltage will jump above 13 volts for a few minutes. Unlike an ICE there is no energy drain when when you start a Leaf so there is not much of a load on the battery. Other reason I have for thinking we are over charging is that I have a 1 kilowatt off grid solar that I USE to charge my Leaf with hooked to a timer that cycled on and off 24 times a day. Cooked the 12 volt battery in 10 months. Not doing that any more.I'm sorry, but overcharging is just about the last thing a Leaf accessory battery experiences as a cause of death. I think that you're close, though. I believe that it's all the times the 12 volt battery gets very low and is then charged up, but it isn't the charging that kills it - it's the being run nearly dead. Lead-acid batteries HATE that...