12 Volt Battery Management; Houston, We've Got a Problem

Ya, thats right 12 volt battery, not the big expensive traction battery. The little (not so cheap probably around $100) lead acid battery.

Now that many are hitting the 18 months to two year range in ownership, we are starting to hear a lot of people getting dead 12 volt batteries.  Since the LEAF is very much a computer on wheels, an unreliable 12 volt power source on the LEAF is causing just as much weirdness as an unreliable 12 volt power source would cause weirdness on your home computer.

One person who drives a lot as a regional manager for a major wireless phone provider had his LEAF sitting over the holidays for just 3 days. Came out and car would not boot up.  Got all kinds of weird dash messages. Instantly realized it was a dead 12 volt battery. He measured it and it was in the 5 volt range!!  He charged up the battery and now everything is fine. No seemingly permanent issues other than a 12 volt battery that has probably lost at least a few days of storage now.  Now, the person in question did store his LEAF outside and it was during one of the coldest periods we have had this winter but we are talking nothing lower than the mid 20's.  IOW, a balmy winter day for most of the Midwest!

The other thing is that he did what he was supposed to do.  He parked it unplugged with about a 60% SOC.  The LEAF was supposed to give the 12 volt battery a small boost, the another recharge in about 5 days which is supposed to be enough to keep the battery going. But it did not work and he is now one of nearly a dozen reports in the last two months of DOA LEAFs where the cause was eventually traced back to the 12 volt battery.

I then decided I needed to monitor mine since my LEAF is 12 days away from its 2nd birthday.  I checked it and found it to be about 12.54 volts but this was after it had been driven about an hour before.

From this chart, I would be at what is really considered the bare minimum a lead acid battery should be at for long life. Remember, lead acid wants and needs to be fully charged at all times.  In a regular car, the battery is used to start the car and as soon as that happens, it is then recharged to full almost immediately and in good conditions can last 5-7 years. (Like any battery, in AZ they are good for 3 years due to the heat)

I had no other trips planned for that day and planned light driving the next day so the LEAF was not plugged in.  The next morning, I get up and checked it and it was 12.18 Volts!!  Despite that still being in the "green" part of the charts, I drove a ZENN with lead acid and even deep cycle batteries did not tolerate a discharge that deep (they lasted about 18 months max when discharged below 50%...trust me. after 3 sets of batteries, this I know!)

Now this was 12.18 volts OVERNIGHT!  I immediately turned the LEAF on (still had 65% SOC) and checked the voltage and it was at 13.08 volts which I determined later is probably the onboard 12 volt system regulating the voltage.  I had to do a few short errands that took a total of 20 minutes of driving.  When I got home, I checked the voltage again after 15 minutes and it was at 12.54 volts so I did get a bit of a charge during that period.

I plugged in the LEAF and it went to 13.27 volts. I came back out an hour later and it was at 14.62 volts so obviously was on a charge cycle.  I had a few other short errands to do so at the end of the day, I checked the voltage and it stayed in the 12.75 volt range for the 4 hours before I went to bed that night.

I had to charge overnight to 100% and charge was completed at 3:35 AM so when I checked it at 5:15 AM, the voltage was 12.72.

Over the next week, I checked it randomly never seeing it below 12.5 volts until this morning.  Friday night, LEAF was fully charged with charge finishing at 5:05 AM. Saturday,  I had a short errand ran at 10 AM.  then another at 2 PM and then a quick jaunt to the drug store at 7 PM (round trip length 2.2 miles) SOC level at 60%.  I get up and check the voltage this morning and its at 12.20

The next "scheduled" charge is probably not going to happen for 4 days. I sincerely doubt that my 12 volt battery will last that long although I am doing exactly as I am supposed to do for long term battery storage.  So the situation is that if I let is sit 4 days (Traction battery will charge 12 volt battery every 5 days) then I will probably find a dead 12 volt battery. If its more than 5 days, I will probably be able to start the LEAF thinking I did everything right and being COMPLETELY UNAWARE OF THE PROBLEM just around the corner!
 Problem with that is every time the 12 volt battery deep cycles like that, its suffering degradation and greatly shortening its life.

Nissan, This needs to be fixed!

**Edit** Just a correction here. Have been advised by people smarter than me that if the 12 volt battery is so dead it wont start the car, in most cases it will be too dead to charge the battery on its 5 day cycle. I am guessing it does take a pinch more power to boot up and then open the contactors to energize the traction battery than it is to open the contactors to charge the 12 volt battery without the boot up.  Either way, does not make me feel any better about the situation.

Hopefully, I can dig up a few workarounds until Nissan gets us a fix. Stay tuned!

**EDIT**

A few people have asked if it was prudent to just replace the battery every few years when the capacity starts to wane. I think I would go for a portable power supply instead for two reasons

1)its cheaper! sorry but money is always a consideration

2) portable power supply is versatile and can be used for other things such a cell phone charger when camping (which is the main reason I got mine)

You can get these all over. I think this one came from Harbor Freight a few years ago. I paid like $50.  A replacement battery for the LEAF would probably be close to $100. They are small, light (about 10 lbs or so?) and provides a portable 12 volt power supply to run your electronic gadgets