LEAF's 12V battery behaviors - and why they go bad

[FalconFour]

Anybody tried disconnecting current sensor?

I tried unplugging the current sensor on my 2014 SL today. It does indeed make the 12v system operate at 14v (14.24v exactly, in my case) continuously. It doesn't seem to make any warning lights come on, but it does set the "P1551 000B EV/HEV Battery Current Sensor EVC-165" and "P1557 000B EV/HEV Battery Temp Sensor EVC-173" codes.

Oh, that's actually pretty cool. I think I might do that with mine, see how it goes. Since the Leaf also charges the 12V (rather, it runs the standard "charging" cycle) when it's charging the HV battery, that could do well to maintain the 12V battery. :mrgreen:

Since I posted this original thread, I've had 2 more dead 12V events... I've got it down to a 2-minute minor inconvenience at this point with my little lithium jump pack :lol: But after each one, I find it lasts at least another month or two if you follow it up with a full 12V charge from an external charger (before plugging the car in to charge normally).

Also, I totally agree that 13.6v would've been a fairly more appropriate "float" voltage for storing months on end. They really could've pushed it even higher to maybe 14.0v given that the purpose of the system is to emulate an alternator, and for decades upon decades, the car just ran at 14.4V (if not higher, less regulated) all the time it's running. If the Leaf's advanced management is supposed to make them last longer (not to mention the complete lack of cranking demand), then why would Leaf owners so frequently run into batteries that only "lasted" a shorter time than an '80s Toyota? The "advanced" system definitely does not serve its intended purpose.

 

[VitaminJ]

Could it be that Nissan originally intended for the car to come with a LifePO battery? 14.4v is a weird voltage to charge a lead-acid battery, pretty much every car's 12v system nowadays runs at 14.7v when powered on. LifePO 4 cells are 14.4v fully charged. There has been some talk already of the charging routine being more closely matched to a lithium-based battery.

 

[Durandal]

Could it be that Nissan originally intended for the car to come with a LifePO battery? 14.4v is a weird voltage to charge a lead-acid battery, pretty much every car's 12v system nowadays runs at 14.7v when powered on. LifePO 4 cells are 14.4v fully charged. There has been some talk already of the charging routine being more closely matched to a lithium-based battery.

That's a very good point. I certainly intend on swapping my Pb battery for a LifePO battery once the Pb battery fails. I do charge it every couple of months on a 2a charger when I think about it to desulfate the battery a bit.

 

[arnis]

Disconnecting current sensor takes less time than refilling washer fluid.
I suspect 2011 Leaf will do the same. This is how fail-safes should operate according
to engineering standards. But still should be verified (Nissan's engineers are questionable).

I will not get into multiple page discussion again (can be found on forum) why almost all
newer vehicles have lower voltage, including Leaf.

Those who want can use previously mentioned trick to get voltage higher. It will overcharge
battery in heavy use scenarios. Those who drive less might indeed benefit from that.
I would only recommend this for those who ran their 12V battery dead (excl OBD adapter problem).
In hot weather I would suggest checking electrolyte level once a month.

Disconnecting current sensor is not necessary below +3C (+37F). Error code is low priority (otherwise
there would be a notification on the dash).

PS! Expect brighter halogen headlights, also shorter lifetime. No effect on LEDs.


PS! 14.24V is much better for failsafe than I expected (14.4V). It appears that it also defaults temperature compensation
to somewhere around 20-25C (norm value for failsafe). Does make sense as temp sensor is also there.

12V systems are not intended to run at 14.7V nor 14.4V. There is no fixed voltage 12V systems are intended for. At all!

 

[VitaminJ]

That's a very good point. I certainly intend on swapping my Pb battery for a LifePO battery once the Pb battery fails. I do charge it every couple of months on a 2a charger when I think about it to desulfate the battery a bit.

Mine died over the weekend, brought it back to life, but I just ordered this as a replacement:
https://www.amazon.com/gp/product/B01J9XN49M/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Gens-Ace Tattu is about the best brand of lithium battery I've ever used. I have sold hundreds of them all over the world and haven't had a single failure.

12V systems are not intended to run at 14.7V nor 14.4V. There is no fixed voltage 12V systems are intended for. At all!

Maybe things are different in Europe but every single car built after 1986 that I've put a multimeter on, be it German, American, or Japanese (e: or Swedish), registered 14.7v with the engine running unless something was wrong.

 

[powersurge]

Although Lithium, a 64WH battery is tiny. It is used to start motorcycles. You are installing it at your 12 volt accessory battery?? After using the lights and a/c, your battery will be dead....????

 

[VitaminJ]

Yes, we will see if it works or not. Though, the AC runs off the main traction battery, the headlights and accessories run of the 12v battery. The 12v battery dies because it is kept at the wrong voltage and sulfates, not because it is drained of all energy. Tattu make a few sizes of that battery, I went for the cheapest and lightest.

 

[BrockWI]

So exactly where is the current sensor wire that is easy to pop on and off?

 

[arnis]

So exactly where is the current sensor wire that is easy to pop on and off?

Negative 12V battery terminal. Sensor itself is integrated into the terminal.
Plug should have 4 wires I believe.

 

[LeftieBiker]

Yes, we will see if it works or not. Though, the AC runs off the main traction battery, the headlights and accessories run of the 12v battery. The 12v battery dies because it is kept at the wrong voltage and sulfates, not because it is drained of all energy. Tattu make a few sizes of that battery, I went for the cheapest and lightest.

The A/C and heatpump compressors run off the main pack, but the blower runs from the 12 volt system. As for Nissan originally intending to use a lithium battery, there is more evidence that they just intended to use a larger lead-acid battery, as larger capacity batteries seem to stay better charged.

If I get another Leaf, I'm definitely going to wire the voltage sensor to a switch, so I can just "tell" the car to charge the accessory battery, when I want, for as long as I want. I'm sick of having to connect and disconnect a battery maintainer.

 

[Durandal]

I agree, that may be too small. The vampire load may drain this fairly quickly. I think you'd want at least 200Wh of storage on the 12v side. Let us know how it works out.

 

[arnis]

Yes, we will see if it works or not. Though, the AC runs off the main traction battery, the headlights and accessories run of the 12v battery. The 12v battery dies because it is kept at the wrong voltage and sulfates, not because it is drained of all energy. Tattu make a few sizes of that battery, I went for the cheapest and lightest.

The A/C and heatpump compressors run off the main pack, but the blower runs from the 12 volt system. As for Nissan originally intending to use a lithium battery, there is more evidence that they just intended to use a larger lead-acid battery, as larger capacity batteries seem to stay better charged.

If I get another Leaf, I'm definitely going to wire the voltage sensor to a switch, so I can just "tell" the car to charge the accessory battery, when I want, for as long as I want. I'm sick of having to connect and disconnect a battery maintainer.

Compressor and PTC element run on HV battery.

Why a switch? I remember that everybody was whining that 13.xx is too low and battery should constantly be trickle charged at 14.xx otherwise it will definitely die due to sulfation.
Just remove the plug and battery will be charged/trickle charged at 14.xx while driving or charging.
Why switch? Is 14.xx too much now? Some already want to keep it at 14.7V :lol:

And it's current+temperature sensor, not voltage. I think it defaults to higher voltage mode due to the fact that it can not measure
temperature. Therefore it is more healthy to disconnect temperature sensor pins and wire a resistor with a value that sets battery
temperature to 0C (value can be found from the diagnostics manual). There will be no error messages then

 

[VitaminJ]

Well when the car is running I believe the 12v battery starts getting 13v from the main pack and it can supply up to 135A (!) through that converter which means everything is powered by the main pack but the 12v battery acts as a nice buffer, and allows accessories to work while the car isn't "on." While this is fine and dandy the lead acid battery needs more than 13v to actually take on a charge. The OP of this thread explains it pretty clearly:

The problem here is that the 12V battery is maintained at a 13.0V trickle charge with a very brief 14.4V boost charge. First of all: 14.4V is the typical charging voltage for lead-acid batteries. Lower than that, they either charge very slowly, or they don't charge at all. There's a threshold voltage that has to be exceeded in order to actively charge the battery. It's possible that the 14.4V charge is continued until the battery is only absorbing a low number of amps, before it drops down to 13.0V.

A LifePO can take on charge at 13v, and with a boost to 14.4v to give it a little exercise. As long as I don't leave the preheat going for hours and hours and as long as I don't leave my headlights on for a week, I should be good. We shall find out collectively! I will have to be careful about leaving it for more than a few days, if the LifePO gets drained it will be ruined.

 

[LeftieBiker]

Why a switch? I remember that everybody was whining that 13.xx is too low and battery should constantly be trickle charged at 14.xx otherwise it will definitely die due to sulfation.
Just remove the plug and battery will be charged/trickle charged at 14.xx while driving or charging.
Why switch? Is 14.xx too much now? Some already want to keep it at 14.7V :lol:

I think that 14.2+ volts can be too much for driving with just the radio on. There is no need to go from undercharging the battery to cooking it.

 

[mamarley]

Why a switch? I remember that everybody was whining that 13.xx is too low and battery should constantly be trickle charged at 14.xx otherwise it will definitely die due to sulfation.
Just remove the plug and battery will be charged/trickle charged at 14.xx while driving or charging.
Why switch? Is 14.xx too much now? Some already want to keep it at 14.7V :lol:

I think that 14.2+ volts can be too much for driving with just the radio on. There is no need to go from undercharging the battery to cooking it.

14.2 volts won't cook the battery. Most ICE cars run the 12v system continuously at 14.4v and the Leaf's 12v battery is just a normal automotive battery.

 

[arnis]

Clearly both of you don't understand s**t about how energy flow works.

If you have fresh+depleted 55Ah 12V battery and you supply it with 13V it will absorb charge at
above 100A rate for short period of time (depends on temperature). With ideal condition
is it possible to max out Leaf's 12V energy supply module, even at 13V mode.

12V batteries on any vehicle (except very old vehicles that didn't have voltage regulators
on alternators, aka at least 20 years old) CAN NEVER NOTICE ANY LOAD VEHICLE 12V SYSTEM HAS!
The only way is to reach supply device's maximum limit. This will result in voltage going below regulated level.
This actually happens on some more advanced vehicles (for example BMW) that have PTC heaters for comfort.


I've already gave all links to all kind of research papers that all say the same. (not BatteryUniversity source-less links).

PS - Leaf keeps 12V battery at 14.5V mode for all those hours Leaf is charging and it is near freezing (or below) outside.
Even the radio is not on. Therefore it should explode or cook or whatever else you expect to happen.

PS - all latest greatest BMW-s have regen that push 15.6V into 80% charged 12V battery while decelerating.
And as far as I know average 12V battery lifetime on those is above 5 years. AGM type. No explosions.
And yes those keep their 12V at around 13.2-13.3V after certain charge state (80%) has been reached.
Usually 15 minutes of driving.
Leaf unfortunately is not smart enough and is not capable to detect 12V battery charge state. Even though
it has current sensor it doesn't store any data to calculate SOC. On the other hand replacing 12V battery is DIY procedure.
On BMW-s it REQUIRES coding. If not done new battery will be ruined fast. Luckily those batteries are hardly ever
replaced. I've seen some older than 8 years and still going strong.

YES all latest high-end BMW-s have regen. Weak (3kW). Something like Leaf-s 1-bubble regen.

 

[VitaminJ]

Charging my lead-acid 12v battery: 14.7v

 

[LeftieBiker]

So, Arnis, you assume that the current sensor (I had mistakenly assumed it was a voltage sensor, because that makes more sense to me in the context of charging a battery) was put there for no good reason at all? OK, but I'm going to assume that it is less than optimum to keep an accessory battery at maximum charging voltage almost all the time the car is On. ICE charging systems, last I knew (and my knowledge may be out of date now), cut the accessory battery out of the charging circuit briefly when its voltage measures optimum, adding the charging current back when it drops to another preset voltage. I'm going to stay with my idea of a switched current sensor, with the hope that it wouldn't be needed in a 2017 Leaf anyway.

The Leaf, BTW, is now in Third place on my Next Car list, after the Ioniq and Bolt. If the 2017 Volt proves reliable and they offer great leases, that may bump the Leaf to fourth, unless it's too hard for me to get in and out of it...

 

[FalconFour]

I will have to be careful about leaving it for more than a few days, if the LifePO gets drained it will be ruined.

Aside from Arnis saying that a Pb battery will take on charge at 13.0V (very minimally, and only when near completely depleted, and only if it's a totally fresh, non-degraded battery, sure! It'll charge to around 40% and then stop accepting charge ) this is the only thing I can find worth chiming in on :lol:

It'll run the same 14.4v->13.0v cycle (or, with disconnected sensor, 14.4v flat) any time the HV battery is engaged, which also includes preheating.

Good points made, all around. In fact, I added that tiny lithium battery to my Amazon wishlist, as it's just past the realm of affordability for me, but could serve as a good replacement once my 12v battery more formally dies...

 

[arnis]

So, Arnis, you assume that the current sensor (I had mistakenly assumed it was a voltage sensor, because that makes more sense to me in the context of charging a battery) was put there for no good reason at all? OK, but I'm going to assume that it is less than optimum to keep an accessory battery at maximum charging voltage almost all the time the car is On. ICE charging systems, last I knew (and my knowledge may be out of date now), cut the accessory battery out of the charging circuit briefly when its voltage measures optimum, adding the charging current back when it drops to another preset voltage. I'm going to stay with my idea of a switched current sensor, with the hope that it wouldn't be needed in a 2017 Leaf anyway.

No. ICE vehicles do not don't cut the accessory battery out of charging circuit. But alternators voltage regulator can lower the output voltage so that battery is not charged (exactly what BMW does for example in full-throttle situation to get more acceleration).

14.2V is far from maximum. Also there is no such thing as universal maximum charging voltage. There is a reason why Leaf switches to 14.4-14.6V mode due to cold temperature. It should be even more when it is even colder but that makes things more complicated (Leaf does not have PWM control for lightsources like headlights, therefore they will just burn out).

One thing that sensor does it switches from higher voltage mode to lower voltage mode when current drops to predefined level.
And it does not take into account battery degradation (appears Nissan's engineers are consistent with their mistakes :lol: )

Aside from Arnis saying that a Pb battery will take on charge at 13.0V (very minimally, and only when near completely depleted, and only if it's a totally fresh, non-degraded battery, sure! It'll charge to around 40% and then stop accepting charge ) this is the only thing I can find worth chiming in on :lol:

Actually it will charge to about 40% very rapidly, an hour max. Lets assume summer and non-sulfated 2 year old battery.
13.0V will result about 75% SOC if kept for 5-20 hours, depending on many factors, including battery additives (calcium, etc)

I will explain once more. All newer vehicles mostly have at least current sensor or IBS. And it is emission based upgrade (better economy) plus prolongs battery lifetime.
Keeping system voltage at predefined high level (14.3V for BMW) will result in parasitic load. This means .x% less range for Leaf and .x more fuel consumed per day on ICE vehicle. Also for start-stop vehicles this sensor is vital for keeping battery at optimal minimum SOC.
It's true that before this era battery was kept at 14.2-14.5V as it was more-or-less most universal voltage. It had efficiency problems but that was not a big deal 15+ years ago.

It is safe to remove that current sensor. It will result in higher average SOC.