Removing 12v battery to charge Leaf

Hi all,

If I remove my 12-volt battery and charge/maintain it inside my flat, will the car lose any saved settings when I return the battery to the vehicle several hours later? Is this approach recommended?
I don't have access to main electricity as I am just using on street parking so using a trickle charger is not possible.
I'm wondering whether turning on/driving the vehicle everyday is enough to keep the 12v maintained or whether I need to invest in a battery maintainer.

Kind regards,
Mark

You will lose the settings, and that's a huge amount of work for the benefit! Your best bet is to replace the OEM 12 volt battery with a higher capacity AGM battery. The group number is 51R. The car should also do a better job of keeper the higher capacity battery charged. Fully charge it before installing it in the car. The cheaper, if less easy or likely to work fix, is to hardwire a good 12 volt solar battery maintainer to the 12 volt battery (the lighter socket is off when the car is off so you can't just plug it into that). This is assuming that you can park the car in the sun at least a few days a week.

maybe you should look at a solar battery tender ....link...https://www.batterytender.com/solar-panels

Given your circumstances, I'd just drive and see how you get on. Get a battery load tester that will show you the true health of the battery (not just voltage) and use it periodically so that you're aware of any degradation before it becomes a problem for the vehicle. If the battery does get weak I'd follow Leftie's advice and replace with an AGM. I think this approach is easier than repeatedly disconnecting the heavy battery and hauling it in and out of doors for charging episodes.

Nubo said:

Given your circumstances, I'd just drive and see how you get on. Get a battery load tester that will show you the true health of the battery (not just voltage) and use it periodically so that you're aware of any degradation before it becomes a problem for the vehicle. If the battery does get weak I'd follow Leftie's advice and replace with an AGM. I think this approach is easier than repeatedly disconnecting the heavy battery and hauling it in and out of doors for charging episodes.

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+1

Just drive the Leaf and charge its traction battery as necessary. I drove my 2011 over 50,000 miles, 2015 over 80,000 miles, and 2019 over 17,000 miles so far. I have NEVER used an external 12V battery charger with them even though I routinely park for extended time at my office or the airport. When I replaced the OEM battery in the 2011 and later in the 2015 (with deep cycle AGM battery in each case), I installed the battery in the evening and plugged the car in to charge the traction battery overnight. The 12V battery is charged by the DC-DC converter whenever the traction battery is being charged, when the car is in "Ready" mode for normal driving, and periodically when the car is parked and completely turned off.

Just drive the Leaf and charge its traction battery as necessary. I drove my 2011 over 50,000 miles, 2015 over 80,000 miles, and 2019 over 17,000 miles so far. I have NEVER used an external 12V battery charger with them even though I routinely park for extended time at my office or the airport. When I replaced the OEM battery in the 2011 and later in the 2015 (with deep cycle AGM battery in each case), I installed the battery in the evening and plugged the car in to charge the traction battery overnight. The 12V battery is charged by the DC-DC converter whenever the traction battery is being charged, when the car is in "Ready" mode for normal driving, and periodically when the car is parked and completely turned off.

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Your use case is common, Gerry, but it isn't the only common one. Some/many Leafs under some conditions don't do a good job of charging the battery. I guess it's possible that the OP is just being a bit OCD about this, but it's more likely that they have had trouble with a weak or dead accessory battery. Checking the rest voltage or getting a battery tester is the way to go if there is no problem now, but if there is one then it needs to be addressed.

markrshort said:

Hi all,

If I remove my 12-volt battery and charge/maintain it inside my flat, will the car lose any saved settings when I return the battery to the vehicle several hours later? Is this approach recommended?
I don't have access to main electricity as I am just using on street parking so using a trickle charger is not possible.
I'm wondering whether turning on/driving the vehicle everyday is enough to keep the 12v maintained or whether I need to invest in a battery maintainer.

Kind regards,
Mark

Click to expand...

Mark,

If you are asking about the 12V battery just because there are numerous threads on this forum that note issues with the 12V battery charging algorithm, then I suggest you just use your car normally and test the 12V battery once in a while. As you can see from my previous post, there should be no need to routinely trickle charge your 12V battery unless there is a problem with your car or your use pattern does not keep the 12V battery charged.

If you think you have issues with your 12V battery now, then test it or get it tested and replace it if it is weak. If it is weak, then test the float voltage of the 12V system while the car is in "Ready" mode (ready to drive normally). The float voltage should be about 13 volts and will vary a little with ambient temperature (higher if it is cold). It should be between 14 and 14.5 volts immediately after turning the car on and will remain high until the 12V battery charging current drops below a threshold which causes it to drop back to the normal float voltage of about 13.

markrshort: Without posting the model year, mileage, your location, and WHAT your problem is with the current 12V battery, the experts here are shooting in the dark.

How about some details?

If you think you have issues with your 12V battery now, then test it or get it tested and replace it if it is weak. If it is weak, then test the float voltage of the 12V system while the car is in "Ready" mode (ready to drive normally). The float voltage should be about 13 volts and will vary a little with ambient temperature (higher if it is cold). It should be between 14 and 14.5 volts immediately after turning the car on and will remain high until the 12V battery charging current drops below a threshold which causes it to drop back to the normal float voltage of about 13.

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Have we ever seen a Leaf that has abnormal accessory system voltages while in Ready Mode? The issue seems to be mainly that when you plug the car in, the voltage will drop too soon from the bulk charge voltage of 14+ volts, and will quickly settle into the float mode of about 13 volts, thus not really recharging the accessory battery. Then, if you leave the car plugged in after charging ends, the accessory battery eventually gets drained. The test that will identify both chronic undercharging and an abnormal vampire drain is the rest voltage measurement, with the car sitting undisturbed, hood open, door closed, for at least 15 minutes. Anything under 12.4 volts indicates that the accessory battery is not even nearly close enough to 100% charge.

Hi all,

Thanks for all this very helpful information. I've just got the car back from an independent specialist and he said the 12v was at 74% capacity when he put it on charge so it seems that my usage of the car(during lockdown) is leading to 12v drainage.
Will Leafs fault on startup with a battery that only kicks out under 13volts on float voltage?

In order to rule out a weak battery, I've ordered a cigarette lighter voltmeter so I will be able to monitor the volts to see if the float voltage drops below 13. If it does then I guess I will have to get an AGM battery(kicking myself I didn't do this when I last replaced the battery).
Can anyone recommend a specific battery in this case?

Thanks again,
Mark

Just been doing a bit more reading. Running the wiper blades on their slowest delay apparently sets the voltage to around 14 and puts charge into the 12v. Any idea how long I would have to do this for? e.g how many minutes for 1% of battery capacity (roughly!). Could this approach damage the battery if the battery got to 100% and I kept putting 14 volts in? If I used a resting voltmeter reading before to see if I am under 13 volts. If so I could then run the blades for X number of minutes to maintain the battery charge without going through the hassle of hauling my battery into my top floor flat. Good theory or not?
This would just be a temporary measure while i'm hardly driving the vehicle. I also had no idea that I had to unplug the vehicle from a charger once finished so this was probably the cause of the chronic drain! I was leaving my vehicle plugged in all day at work

Please note, I have had the well known 'no braking power upon start-up' fault so i'm feeling a bit nervous about driving it at the moment.

Further research shows from watching this video (https://youtu.be/ipEzK1yzxHY?t=6760) that the DC-DC converter puts about 4 amps into the 12 battery when running at 14volts. Looking at this 'determining charge time table' (http://batteriesbyfisher.com/determining-charge-time) and its shows the following: with 5 amps, my 500 amp battery with a current reading of 12.35v will take about 2.5 hours to charge fully. This shows the initial bulk charge upon startup for a few minutes isnt going to be at all adequate to recharge the battery fully once it gets low from the parasitic drain (e.g you've left it parked for a long time or you're leaving the car plugged into a charger overnight). When charging the traction on a fast charger do you get 14volts through the system for the FULL duration? if so that would keep it topped up.
It seems the answer is I need to get some miles into the car, which is a waste of time when working from home, and charge the car regularly or sit there with the wipers on for 20 mins every so often. The algorithm must assume(wrongly, in some cases) that the aux battery charge level is never that low and just needs tiny top up each time. I may be wrong on some or all or these theories. Any thoughts anyone?
Thanks again for the info.

I bought my 2013 Leaf two years ago and ended up replacing the 12v battery with an AGM deep cycle 90 days later. Since then, I have often left the car plugged in to the 120v charger for days without driving it and never had a problem (I monitor the 12v charge level w Leaf Spy). If you're not experiencing an actual problem, I wouldn't make yourself crazy trying to anticipate one. As someone else mentioned, knowing the year, SOH of the main battery and if you're experiencing issues would be helpful.

The float voltage of the 12 volt system will normally read fine, even when the 12 volt battery is undercharged. Are you leaving the car plugged in for long periods after the car finishes charging?

markrshort said:

Further research shows from watching this video (https://youtu.be/ipEzK1yzxHY?t=6760) that the DC-DC converter puts about 4 amps into the 12 battery when running at 14volts. Looking at this 'determining charge time table' (http://batteriesbyfisher.com/determining-charge-time) and its shows the following: with 5 amps, my 500 amp battery with a current reading of 12.35v will take about 2.5 hours to charge fully. This shows the initial bulk charge upon startup for a few minutes isnt going to be at all adequate to recharge the battery fully once it gets low from the parasitic drain (e.g you've left it parked for a long time or you're leaving the car plugged into a charger overnight). When charging the traction on a fast charger do you get 14volts through the system for the FULL duration? if so that would keep it topped up.
It seems the answer is I need to get some miles into the car, which is a waste of time when working from home, and charge the car regularly or sit there with the wipers on for 20 mins every so often. The algorithm must assume(wrongly, in some cases) that the aux battery charge level is never that low and just needs tiny top up each time. I may be wrong on some or all or these theories. Any thoughts anyone?
Thanks again for the info.

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If you can't use a plug in battery maintainer with the car, then a solar charger hardwired in may help, although they are often of poor quality. A 51R AGM battery may also work, although if more charge is being drained than is going in, the issue will remain.

If anybody want to "fully charge 12V battery" - just disconnect current sensor plug right on the negative battery connection clamp.
Computer will default back to 14.4V. After that just plug it back. Error code will be stored but who cares.

arnis said:

If anybody want to "fully charge 12V battery" - just disconnect current sensor plug right on the negative battery connection clamp.
Computer will default back to 14.4V. After that just plug it back. Error code will be stored but who cares.

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Thanks - I'd forgotten about that trick. The car would still have to be driven enough to charge the battery at the bulk rate, but it's worth a try.

No need to drive Leaf. It will charge at 14.4V even when stationary and just "READY" mode or "CHARGING"

Thanks everyone. The car is a 2016 Leaf tekna with 55900 miles on the clock.

In the last 5 months I've had about 6 breakdowns - all to do with the startup braking problem whereby when you start the car the dashboard lights up like a christmas tree (yellow abs light, yellow brake warning light, red main warning light). If you put your foot on the brake, it goes virtually to the floor and you get abs pulsing sounds plus a horrible grinding noise. If you were to pull away and tried to stop the car it would take A LOT longer to stop and would require a lot more force applied to the brake. When the RAC man came to have a look he checked the voltage on the 12v and it was at only 12.27 volts. After leaving the car on for a bit and then resetting the car it seemed to rectify the problem. So I assumed the battery was not taking enough charge from the DC-DC convertor anymore and I needed a new battery.
I got a new battery(Varta lead acid) fitted but two days later I had the same braking problem. This time the problem occurred about 30 seconds to a 1 minute into the journey(scary! lucky i was on a quiet lane and not going fast) the dash lit up and I lost braking power. This time I had my pregnant partner in the car with me and shes lost all confidence in the car and rightly wont go in it anymore. The fact that the brakes failed after startup makes me wonder if this has got anything to do with the 12v at all and maybe its another design problem with the car. Possibly the firmware on the intelligent braking unit? I asked about this at the dealership and they said it didn't apply to my car despite this link (https://flipthefleet.org/2018/leaf-brakes-failures/) suggesting that it affects models manufactured between March 2012 and Feb 2016 (mine was manufactured in Feb 2016).

So without any other options i'm considering upgrading to an optima yellowtop. Can i ask why would an AGM perform better than a lead acid in a Leaf in particular?. Do they retain a steady voltage despite a descreasing SOC % or is the benefit more to do with their low internal resistance and its ability to take charge better.
My other question would is .. does the leaf warn you when the 12v battery charge is low? The software that manages the charge of the 12v seems totally inadequate and can lead to this dangerous problem(?).

I'm currently working with someone from flipthefleet who is going to provide me a report on his findings about other leaf owners with the same problem. I'm hoping this report alongside my video of the issue will support my case to get a refund on the vehicle from the original dealership. Failing that then i'm taking it to the ombudsman.

Any help more help would be very welcome!
All the best, Mark

AGM - real AGM, not Chinese "AGM" - batteries can be drained lower, and are usually higher capacity for the size compared to starting batteries. They also seem to accept more charge in a short time with the Leaf; it's speculated that the car was designed for a higher capacity battery, and the charging system 'stops short' and switches to float mode as the voltage on the little starting battery rises quickly during bulk charge.

No, no low voltage warning I'm afraid. Maybe there is a vampire drain in the electric brake booster as you speculate...