Bob wrote:There are two possible reasons for battery problems: either the system is not charging the battery correctly or the Leaf is leaking current out of the battery while parked. Either one will cause the battery to fail prematurely.
In fact, it appears both are likely involved here.
Bob wrote:It is very easy to test for Leaf leaking current out of the battery. In the Leaf service manual, they call this "Dark Current". Just put an ammeter in series with the 12V battery and turn off everything in the car. According to the service manual, it should consume less than 50mA. The battery is rated for 45 amp-hours, so it should last for roughly 900 hours (5 weeks) with 50mA of leakage. On top of that, the Leaf tops off the battery for 5 minutes every 120 hours from the traction battery, so even if you park the car for a month, the battery should not go dead.
I've already made this measurement in my MY2011 LEAF
But this measurement was done under only one scenario and with only one set of firmware. It is entirely possible that there are conditions which can occur which cause some larger loads to be improperly left on. In fact, it appears from some of the reports with MY2013s and later that this is the case.
Bob wrote:It is very easy to test for improper charging. Just put a voltmeter on the battery while the car is on. It should be approximately 14.5V, indicating that it is being charged correctly. If it is below 13.5V, then the charging system isn't working correctly.
I think your approach here is a bit old-fashioned. The charging system in the LEAF (and apparently other recent cars) does not keep the charger at 14.4V for the duration of the time the vehicle is on. It attempts to replace only the charge which has been lost and then quickly drops down to a float voltage of 13.1V. Herein lies the real problem. It seems to not properly account for HOW LONG the LEAF was off, and generally does NOT restore the battery to a full charge level. The issue is premature sulfation of the battery and early failure.
Bob wrote:If charging is good and dark current is low, then it was just a bad battery. But if either of the other things is bad, changing the battery won't solve the problem.
It's not so simple as you imply. It seems the charging algorithms coded into the LEAF's 12V system work fine for some users and not as well for others, depending on driving regimes. In any case, the system works the way it does and, to my knowledge, no one has reported an actual "failure" of the 12V charging system. Rather, I feel it is simply poor software design (the hardware seems extremely robust to date).
There have been more than a few batteries which have failed with a shorted cell, both from Japan and from the U.S. That is likely just due to poor quality control.