Sunday, January 6, 2013

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 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!


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


  1. Definitely an issue, an AGM battery in a BEV should last the life of the car.. there are no heavy starting loads and the temperature under the hood is much lower than a conventional car.

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  2. Herm; I agree with you 100%. As we all know, extreme heat like Phoenix can shorten a battery's life quite a bit but these are batteries in mild climates less than 2 years old that are starting to become unreliable. I think the huge swings in SOC is simply not good for lead acid. Either a change to a Li chemistry or a change to the charging cycle needs to be done here.

  3. 12 volt lead acid batteries can be given a longer life by using a charger with a regen . This puts a high current short pulse thru the cells that brakes down some of the insoluble lead sulfate. I Have used one for years even with batteries that have been declared dead and am convinced they help.
    The in I use is made by Vector or Victor .
    There is really no need for a 12 volt battery in the Leaf..There are plenty of 400 to 12 volt converters around , or Nissan could easily implement one. It probably has something to do with so called safety regs..
    I built myself a 240 volt adapter in 30 minutes after getting my LEAF and it is still working fine ( 20 months, 12,000 miles ). Cost is minimal <$100 so why can't everyone have one or even better why didn't LEAF supply it.

  4. Ron; the separate 12 volt system is all about safety. it allows the large, high voltage traction pack to be electrically isolated in case of emergency. the issue here is the way the 12 volt battery is allowed to discharge so deeply and then allowed to sit that way for long periods of time. Li would not have that issue. In fact, the chemistry is taylor-made for the way Nissan uses it. It prefers to be in the middle SOC range where Nissan's 12 volt battery seems to spend most of its time. I am guessing cost is the reason why Nissan went cheap with lead

  5. So, would it be prudent to replace our 12v batteries every two years to avoid a dead Leaf? (I'd rather spend $100 than be stuck somewhere) - what do you think? steve in seattle

  6. Steve; right now its hard to say. On the one hand, most people are not having a problem but that does not account for the people who are doing exactly as they should who are seeing dead 12 volt batteries.

    Right now, I have been checking the voltage on my battery as much as possible. What I am finding is that as long as you use your car frequently, you will be ok. Now, the car still does not charge up the battery as much as it should but the demand on the battery is pretty small so a battery in "great" condition is not necessary.

    So, I would say to you is if you drive the car at least daily, you have little to worry about. It might not be a bad idea to take the battery to any battery store. they can test it to see how much life it has. If you are in a position where the LEAF may sit for 3 days or more, I would get a jump box. Cheap insurance. I got one at Harbor Freight for like $50. i will post a pix of it.

    I originally wanted to see how the voltage went when the LEAF sat for a while but that has become impossible. Every once in a while, i may only go out once briefly in a day, but usually its out 2-5 times a day and 30-60 miles so that is out.

  7. Hello, I'm new to this and not technically inclined at all. Just as I hit my 2 year mark with my Leaf last month. A weird thing started to happen. After I started the car, put my foot on the break, put it in "R" the car began reversing as though my foot was NOT on the brake. In fact, at the same time, the brake pedal went soft and I had to put it in "Park" halt any further movement. This happened two days in a row, thankfully I didn't hit anyone! At first I thought I was one of those people you read about whose foot "slipped" off the brake onto the accelerator but after the second time I knew it wasn't me. The next morning I went on an errand and when I returned to start the car it wouldn't and an error message flashed "T/M, take car car to dealer" or something like that. Nissan told me that the 12V was dead and since it controlled the computer my car was not functioning. This is a dangerous situation. They changed the 12V and said it worked fine. Yes, for now. I did a google search and found one other person who encountered the exact same problem. This is not a good thing. I drive the car daily and pretty much exhaust the charge every day. I live in a warm climate, Hawaii, and there are scores of Leafs (Leaves?) on the road. Frankly, I'm uncomfortable driving this car and I go up and down a very steep hill several times a day. How do we know the whole system won't shut down with no backup system such as hydraulics? Any thoughts?

    1. Sounds like the dealer was able to fix the car before anything serious happened but the possibility of being stranded due to the battery still sucks. Have a few with a 2013 that have gone out to find their batteries dead after sitting overnight. Right now I am on cation and will be home tomorrow night. Car has been sitting since the 21st so we shall see how well
      the battery holds up

    2. Sounds like the dealer was able to fix the car before anything serious happened but the possibility of being stranded due to the battery still sucks. Have a few with a 2013 that have gone out to find their batteries dead after sitting overnight. Right now I am on cation and will be home tomorrow night. Car has been sitting since the 21st so we shall see how well
      the battery holds up

  8. I strongly suggest that anyone who is considering a change in electric service providers get everything in writing. The TXU rep cam to my office and gave em the old bait and switch. I was told I would recieve a rate with "no additional charges or fees". Of course there are several! The end result being that I now pay more for my electricity. Read The Contract! Cheapest Electricity in Houston

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