How to Quickly & Simply Charge a Leaf’s Weak 12 Volt Battery

R1200RT said:

Stanton how is that LiFEPO4 battery doing? I am considering getting one from Ohmmu for my 2013 Leaf SL.
Thank you.

Click to expand...

I'm right behind him at nearly 8 years on my Lithium battery, same capacity too (20 AH). I got mine from stark power, but the company has since gone out of business.

knightmb said:

R1200RT said:

Stanton how is that LiFEPO4 battery doing? I am considering getting one from Ohmmu for my 2013 Leaf SL.
Thank you.

Click to expand...

I'm right behind him at nearly 8 years on my Lithium battery, same capacity too (20 AH). I got mine from stark power, but the company has since gone out of business.

Click to expand...

Thank you for the information

I just ordered the Antigravity battery monitor to better track what's happening before I commit to a LiFePo4 battery.

I just ordered an Ohmmu LiFePO4 for my 2012 Leaf after the Walmart EverStart Maxx-51R installed by the previous owner in 2017 began to struggle to hold a charge. I've gotten some very weird lights and error messages and now I just keep the battery on a low maintainer charge until the Ohmmu gets here.

It should be here Tuesday and I'm excited to install it and get on the road. I just bought the car last weekend and am dying to use it.

The Ohmmu was about $100 more than an AGM battery at AutoZone or Advance locally. I think it should be worth it from what I have read. I'll let you know...

The important thing to know is that the new battery may need to be fully charged BEFORE it's installed. The battery maintainer can manage that, but it may take as long as several days (more likely one day).

Ohmmu LiFe battery is installed!
Needed about 12 hours to fully charge before install. Working great.
The biggest difference for install was the size and weight of the new Lithium Iron Phosphate battery (11 pounds) versus the old Lead Acid battery at nearly 28 pounds.
Cost was $349 at Ohmmu website. I saw AGM batteries locally for around $249. If the Ohmmu lives up to the 5 to 8 year (or longer) lifespan as claimed, I think it will be worth the extra cost.
I will update here from time to time.

I just installed my Ohmmu without trickle charging it up. It was $265.30 + $19 which is comparable to an AGM. I was wondering whether trickle charging was necessary. I'm pretty sure it's necessary because I got the PS warning and then the car wouldn't shift into drive. Looking over the threads, it sounds like I needed to trickle charge but I'll just let the BMS do that for me and check in a day or so.

I came back in a day and the Leaf still wouldn't shift out of N. I don't get the chimes and it still says PS. I'm going to try jump starting it from my S (with another Ohmmu in it).

Olsonist said:

I just installed my Ohmmu without trickle charging it up. It was $265.30 + $19 which is comparable to an AGM. I was wondering whether trickle charging was necessary. I'm pretty sure it's necessary because I got the PS warning and then the car wouldn't shift into drive. Looking over the threads, it sounds like I needed to trickle charge but I'll just let the BMS do that for me and check in a day or so.

Click to expand...

The P/S light usually comes on when the car is plugged in and thus can't be driven - the power steering is deactivated.

Olsonist said:

I came back in a day and the Leaf still wouldn't shift out of N. I don't get the chimes and it still says PS. I'm going to try jump starting it from my S (with another Ohmmu in it).

Click to expand...

The LEAF will only charge the 12V battery when in READY mode or when traction battery is actually being charged. Therefore, you need to plug the car in to charge or drive it for it to actively charge the 12V battery. It will not charge the 12V battery when parked and OFF. That is probably why you came back the next day to the 12V battery still dead. The other possibility is a defective Ohmmu battery.

GerryAZ said:

The LEAF will only charge the 12V battery when in READY mode or when traction battery is actually being charged. Therefore, you need to plug the car in to charge or drive it for it to actively charge the 12V battery. It will not charge the 12V battery when parked and OFF. That is probably why you came back the next day to the 12V battery still dead. The other possibility is a defective Ohmmu battery.

Click to expand...

There has been a *lot* of discussion about the Leaf's 12V battery charging algorithm, over the years. It's possible that different model years have different behaviour; but my former 2013 Leaf and my current 2014 e-NV200 would run a short top-up 12V charging cycle on a 24 hour timer. There's some reason to believe that the 24-hour period starts when the vehicle is turned off; so if you use your vehicle daily this 12V "maintenance" top-up will never occur.

Annoyingly, as many have discovered over the years, if a charging session has terminated and the Leaf is still connected to the EVSE, the 12V top-up never occurs -- so this crucially-important battery will go flat within a few weeks (or even within a few days, if it's near the end of its life).

Also, as far as I can tell, on all Nissan EVs, the 12V battery is *not* topped-up whenever you charge the traction battery. Instead, the only convenient way I know to "force" the DC-DC converter to kick in -- and thus to charge the 12V lead-acid battery -- is to turn on the windscreen wipers. I learned this from the first post on this thread! How to Quickly & Simply Charge a Leaf’s Weak 12 Volt Battery

A voltmeter is your friend on this. You can plug an inexpensive one into the cigarette-lighter/accessory hole on your dashboard; you can use LeafSpy; or you can measure at the terminals of the 12V battery. If the battery is at 14.4V, it's charging. It should be above 12V when "resting". And if the battery's voltage ever droops too low (below about 9V) your Leaf is "soft-bricked" until you charge that 12V battery.

As confirmed with my voltmeter, my 2019 SV+ Leaf applies a 13.0V float charge to the 12V accessory battery whenever the car is on (not sure about the windshield wiper trick, I'll have to try that). The voltage initially rises to 14.35V for roughly 90 seconds after the car is started then quickly returns to 13.0V. If the 12V accessory battery gets low (old, extreme cold or accidentally drained by carelessness), that intermittent 14.35V and the 12V float charge may not be enough to allow the accessory battery to recover.

Update: The windshield wiper trick is valid. For my 2019 SV Plus the DC/DC converter will apply 14.35V to the 12V accessory battery whenever the windshield wipers are on.

TronJockey said:

As confirmed with my voltmeter, my 2019 SV+ Leaf applies a 13.0V float charge to the 12V accessory battery whenever the car is on (not sure about the windshield wiper trick, I'll have to try that). The voltage initially rises to 14.35V for roughly 90 seconds after the car is started then quickly returns to 13.0V. If the 12V accessory battery gets low (old, extreme cold or accidentally drained by carelessness), that intermittent 14.35V and the 12V float charge may not be enough to allow the accessory battery to recover.

Click to expand...

Hmmm... 45 seconds of charging at 100A is (45s)(1h/3600s)(100A) = 1.25Ah. That'll help a little but you'd lose ground if that were the only time it were charging. A parked-up Leaf loses roughly 3Ah/day from its 12V battery, according to a blogger. You need dozens of Ah to "top-up" a half-discharged lead-acid 12V battery.

Some say it's a 4-minute charging session of the 12V from the traction battery, once every 24h, on a parked-up Leaf. (4min)(1h/60min)(100A) = 6.7 Ah. That'll be plenty to keep a 12V battery topped-up, unless it is dying of old age.

While you're driving, or just "idling" in drive mode, I *think* the DC/DC converter will kick in if the total current draw of the vehicle (including whatever the battery is accepting) is enough to push the 12V supply below some threshold voltage, perhaps 12.5V? A 12V bog-standard lead-acid battery that's on 2/3 of its charge will float at about that voltage... and whenever the DC/DC converter kicks in it'll be bulk-charging, whoopee! All to say that I *think* the Leaf's low-voltage charging system is designed to bring its lead-acid battery up to at least 2/3 of its charge while driving, and I *think* it'll crawl above that charge-level if you are running the windshield wipers (or cabin heater or any other big current-draw) because that'll cause the DC-DC converter to kick in.

I can confirm that a minute-or-so charge of the 12v battery occurs when you first plug the charging cable in (and presumably daily after that) on my 2013 Leaf.

I learned this when I left my leaf unplugged for three weeks and discovered the 12v battery was shot, and used a voltmeter to explore how the charger behaved.

(My voltmeter is the trusty Fluke 73 I bought from the EE storeroom in college... 4 decades old and still ticking.)

I see some evidence in the plot below that a 40kWh Leaf will run a (roughly) 15-minute top-up charge session at 13V every twelve hours, if it's parked up and *not* connected to a slowcharger. (And maybe it'll run these sessions even when it is connected to a slowcharger, I really don't know.)

The person who provided this plot to me (on the NZ EV Owners FB group) says they were slow-charging from 5am to 7am. The lead-acid battery was charging at 13V for almost all of this slow-charging session. I also see 15-minute top-up sessions at 7.30am and 7.30pm.

The blasts of 14.4V last for only a few minutes. I'm now thinking they're mostly intended to desulphate the battery, rather than to charge it. A very low battery will charge pretty rapidly at 13V; and it won't overcharge at that voltage.

Here's another graph from results on a Lithium battery from Lithiummoto.com and its hard to decipher what the car is trying to do to the 12V battery.

Disconnect the current sensor coming off the battery terminal and the DCDC will keep the aux battery charged at the higher voltage needed to desulfate the plates.
See this post for connector picture, #27