How long will it take the DC/DC converter to charge a dead 12v battery?

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brenton

Active member
Joined
Sep 17, 2017
Messages
25
My Leaf was completely unresponsive, probably a light left on or something. I got AAA to come out and give me a jump start so I could turn the car on. I have the car sitting on and in "Ready" mode, I assume the DC-DC converter has sensed the low 12v battery and is now charging it. How long will it take to get the 12v charged back up? The traction battery is at 23% so it's definitely enough, but I'd like to plug in to my L1 charger soon so I can get to work tomorrow!
 
The Leaf's charging algorithm is unreliable, especially for the 2013 cars. Your 2015 may be ok, but don't count on it. Use an external charger or maintainer to get it recharged fully.
 
LeftieBiker said:
The Leaf's charging algorithm is unreliable, especially for the 2013 cars. Your 2015 may be ok, but don't count on it. Use an external charger or maintainer to get it recharged fully.

I can drive to an auto store and purchase a 12v charger/maintainer but I'm afraid that I won't be able to turn the car back on after I buy it. Is the algorithm reliable enough to have a ballpark idea of when it's safe to turn the car off and still be able to turn it back on again?
 
IF the battery wasn't badly damaged then you should be ok for that trip to the store after an hour or so. If the battery was badly damaged by being drained, then it could be 6 or more hours, or the battery could just die again regardless. It's hard to be more specific than that. My 2013's battery was drained enough, in 2014, to stop the power door locks from working, but I was still able to start it. I still have that battery in it, but use a maintainer often. If yours was so flat that you couldn't start the car with the mechanical key and the key fob RFID chip, then lasting damage is more likely.
 
LeftieBiker said:
IF the battery wasn't badly damaged then you should be ok for that trip to the store after an hour or so. If the battery was badly damaged by being drained, then it could be 6 or more hours, or the battery could just die again regardless. It's hard to be more specific than that. My 2013's battery was drained enough, in 2014, to stop the power door locks from working, but I was still able to start it. I still have that battery in it, but use a maintainer often. If yours was so flat that you couldn't start the car with the mechanical key and the key fob RFID chip, then lasting damage is more likely.

Thanks. I'm going to buy the Suaoki Car Battery Charger for future use but for now I will take a chance after a few hours and plug in the L1 charger overnight. I can jump in the morning if I need to and hopefully driving to work will power it up enough to get me home. Its so annoying that it doesn't tend the 12v when the EVSE is plugged in! Why did they do that? Can I tend the 12v manually with a tender while it is L1 charging?

EDIT: After about 2 hours I went out and turned the car off, plugged in the trickle charger (the standard EVSE that comes with the car) and it tripped the GFCI of my deck outlet. I have been using that outlet for over a year and it's never tripped. But every time I plug in the car, the GFCI trips. I tried with another trickle charger (from a Prius Plug-in) and it didn't trip the GFCI, so I'm trickle charging with that. Why would a low 12v battery trip the GFCI though?
 
Yes. In fact, I mainly use my maintainer while charging. I have the lead installed to terminate in the charging port compartment. Just be careful to unplug it either before charging ends tomorrow, or very soon thereafter.
 
Your 12-volt battery should be completely charged by the time your traction battery is charged. The DC-DC converter charges the 12-volt battery while the traction battery is actually charging so the slower L1 charge will allow more time to get the 12-volt battery fully charged. The DC-DC converter has a high enough output to get the 12-volt battery to at least 1/2 charge in an hour. I think you have something happening with your Nissan L1 EVSE if it is tripping the GFCI. If fact, that might be why your 12-volt battery was dead if the GFCI tripped while charging and the car was left plugged in (but not charging) for extended time. I have never connected an external charger to either of my LEAF's 12-volt batteries. I have jump started them a few times when something caused the 12-volt battery to be discharged, but just depended upon the DC-DC converter to recharge them quickly. In each case, the battery was reasonably well charged after 30 minutes of driving and completely charged after overnight L2 charge of the traction battery.

You can use an external 12-volt charger if you wish, but the DC-DC converter puts out over 100 amperes if necessary to quickly charge the little battery.
 
The issue is not, as I think you know, lack of power from the DC-DC converter. It is charging algorithms that don't always work well. Again, in a 2015 it shouldn't be a major issue, but once a car gets a dead 12 volt battery I suggest people err on the side of caution. I do agree with your theory on why the battery was dead.
 
brenton said:
Its so annoying that it doesn't tend the 12v when the EVSE is plugged in! Why did they do that? Can I tend the 12v manually with a tender while it is L1 charging?

Is that what the 2015 manual says? My 2017 manual section EV-5 "CHARGING THE 12V battery" has three sections: the first says:

The 12-volt battery is charged automatically using electricity stored in the Li-ion battery.
...
3. When the 12-volt battery is being charged, the charge status indicator light on the instrument panel flashes (except when charging the Li-ion
battery or the power switch is in the READY to drive position).
...which, to me, implies that there is a time when both the 12v and Li-Ion batteries are charging (because they are telling the owner that in that particular instance, the dashboard lights will not tell you that the 12v battery is charging).

The second section of EV-5 "While the vehicle is driven" says that the 12v is charged while READY or ON, except when in ACC or transmission in neutral.; but I don't think that is meant to say that the vehicle _only_ charges when READY/ON.
 
Listen to @GerryAZ : he knows what he's talking about.
12v battery chargers/maintainers are a waste of money and time in a normal use case (e.g. drive the car most days).
 
specialgreen said:
brenton said:
Its so annoying that it doesn't tend the 12v when the EVSE is plugged in! Why did they do that? Can I tend the 12v manually with a tender while it is L1 charging?

Is that what the 2015 manual says? My 2017 manual section EV-5 "CHARGING THE 12V battery" has three sections: the first says:

The 12-volt battery is charged automatically using electricity stored in the Li-ion battery.
...
3. When the 12-volt battery is being charged, the charge status indicator light on the instrument panel flashes (except when charging the Li-ion
battery or the power switch is in the READY to drive position).
...which, to me, implies that there is a time when both the 12v and Li-Ion batteries are charging (because they are telling the owner that in that particular instance, the dashboard lights will not tell you that the 12v battery is charging).

The second section of EV-5 "While the vehicle is driven" says that the 12v is charged while READY or ON, except when in ACC or transmission in neutral.; but I don't think that is meant to say that the vehicle _only_ charges when READY/ON.

No my manual doesn't say that, it's just what a ton of people have said on this forum, across several threads regarding the 12V system. After reading it enough times I've just accepted it as a fact, since no one ever questioned that until now. Now I'm not sure!!
 
I'm not sure what the exact claim is above, but the problem is that the car doesn't charge the 12 volt battery adequately when the car is plugged in but not charging, and there is a drain at that time that will kill the 12 volt battery over a longer period. It doesn't have to be a "no charge" situation, just a "not enough charge" situation. The cars also don't always charge the 12 volt battery enough even while driving, unless the wipers and/or climate control are used regularly.
 
Stanton said:
12v battery chargers/maintainers are a waste of money and time in a normal use case (e.g. drive the car most days).
And you ended up with a "12v LiFePO4 battery" in your LEAF exactly how? No way did my 12V battery charger/maintainer cost nearly as much as your "12v LiFePO4 battery".

A waste of time? Yeah.
 
RegGuheert said:
Stanton said:
12v battery chargers/maintainers are a waste of money and time in a normal use case (e.g. drive the car most days).
And you ended up with a "12v LiFePO4 battery" in your LEAF exactly how? No way did my 12V battery charger/maintainer cost nearly as much as your "12v LiFePO4 battery".

One has nothing to do with the other. Replacing my 12v lead-acid with a Lithium was not a "money" decision: I simply didn't want to worry about my 12v going dead anymore (no trickle charge, no checking, no worries). At this point, my LiFePO4 battery has lasted longer than any 12v battery I've ever had...in any car (going on 5 years).
 
Stanton said:
One has nothing to do with the other.
Of course they do. If I had not taken care of the 12-V lead-acid battery of our MY2011 LEAF it would have died years ago. As it stands, it will turn 7 years old in June and is in like-new condition. The battery charger was much cheaper than a battery (or two), but it is certainly more trouble.

You wasted more money than I did, but I wasted more time. I did not "waste both" as you say. I saved money.

It would be best if Nissan had used a better charging algorithm, but they didn't.
 
RegGuheert said:
Stanton said:
One has nothing to do with the other.
Of course they do. If I had not taken care of the 12-V lead-acid battery of our MY2011 LEAF it would have died years ago. .....

Regular Flooded Lead Acid batteries are notorious for failing for Stanton and I living in TX. Every summer when I drive past an Autozone there are at least 3-5 vehicles in the parking lot getting their batteries replaced. NOTE: I said summer and not winter.

Why? Because the average vehicle owner does not check the fluid level in the battery, and in some cases they cannot check the fluid level. This means owners drive around with batteries that dry up in 3 years or less. Why do they dry up? HEAT. HEAT is what kills regular lead acid batteries.

How do people like Stanton and myself solve this problem? We buy either AGM or LiFePo4 batteries that are usually > $300+

You can call it wasting money, but not having to replace 12v batteries every 2-3 years vs 6-10+ years? Hmmmm....I wonder who is really saving money!

I have had similar discussion on Subaru forums and there are individual on there that think just like you. I'll keep claiming warranty and/or replacing the lowest price battery every 2-3 years!!!!
 
As R1200RT said, HEAT is a real killer of flooded-cell lead acid batteries. The Nissan OEM batteries in my 2011, 2015, and 2019 actually lasted longer than average for OEM batteries in my climate because under hood temperatures in the LEAF's are significantly lower than gasoline/diesel engine vehicles. The heat also causes batteries to sometimes fail without warning so I carry a booster battery (jumper pack) or at least cables. I don't like the inconvenience of battery failure so I have been using only premium quality AGM (absorbed glass mat) batteries as replacements for at least 20 years. I have had "premium quality" flooded-cell automotive batteries fail in as little as 6 months of daily use in Phoenix, but typically get 3 to 8 years of use from AGM batteries without needing periodic maintenance (adding distilled water and cleaning corrosion from terminals). Since AGM batteries typically do not vent gas unless overcharged, there is usually no terminal corrosion.

As noted previously, I have never connected an external 12 battery charger to any of my LEAF's. The DC-DC converter charges the 12V battery when the car is in ready-to-drive mode as well as when the traction battery is charging. Since the DC-DC converter can supply over 100 amperes when needed, it will recharge a dead battery enough to start the car in just a few minutes.
 
As noted previously, I have never connected an external 12 battery charger to any of my LEAF's.

It just occurred to me that you haven't needed an external 12 volt charger or maintainer precisely because of your Hot climate. The consistently warm battery that results from sitting in that weather would effectively have more reserve capacity than an identical battery in a colder climate, allowing it to out-wait the 'gaps' in charging cycles from the DC-DC converter that are so common with the Leaf.
 
LeftieBiker said:
As noted previously, I have never connected an external 12 battery charger to any of my LEAF's.

It just occurred to me that you haven't needed an external 12 volt charger or maintainer precisely because of your Hot climate. The consistently warm battery that results from sitting in that weather would effectively have more reserve capacity than an identical battery in a colder climate, allowing it to out-wait the 'gaps' in charging cycles from the DC-DC converter that are so common with the Leaf.

Unfortunately that is not the case. At least in my case. The voltage drops over night on the 12v leaving it in a weakened state. 12.1v-12.3v the next morning. Sulfation occurs. My onboard battery monitor tells me it regularly drops below 40% SOC. Even down to 10%.

The heat causes it to discharge at a higher rate, and recharge at a higher rate boiling the acid. And when repeated often enough, the plates are exposed!!!

I nursed my factory 12v from 2013 until 2022. But I was topping up distilled water twice a year. Before and after the hot season.

With AGM or LiFePo4 this maintenance is not required and they last 6-10+ years.
 
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