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You could just keep one of those small 12v jumper packs (the small li-ion ones) in the car and use it to jump start your car if the 12v battery dies.

Or just replace the 12v battery every two years and not worry about it.
Or just stop a passing dinosaur and borrow their vehicle and jump leads.

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For a jump pack for EVs, I don't think it is really a job for rechargeable batteries. TBH it is just a waste of making rechargeables when you want long life "use-once" throw-away batteries.

For EVs I think it would make sense just to make your own with long life AA cells that can be stored in the car indefinitely. The lithium-iron batteries should last the lifetime of the car;-
*EXPIRY 2037* 12 x ENERGIZER ULTIMATE AA LITHIUM BATTERIES LR6 L91 NEW 1.5v NEW | eBay
(no connection with vendor, ebay example)
 

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You could just keep one of those small 12v jumper packs (the small li-ion ones) in the car and use it to jump start your car if the 12v battery dies.

Or just replace the 12v battery every two years and not worry about it.
I prefer not to put myself in the position of never knowing when it might fail to boot up. I have declared surrender and just put the 12v battery on smart charge overnight once a month. That maintains the 12v DC battery in good condition and not only avoids being stranded but also extends its life and saves having to buy and maintain a small jumper pack as well.
 

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Thanks Donald - food for thought there. I see that they supply a normal 12v battery.

I was testing the charging last night and the charge did not kick in till under 11.70v which seems very low to me. Wonder if this can be adjusted anywhere on the system.
If the Leaf really doesn't start charging the 12v battery (I presume you mean when the car is parked and turned off) until it reaches 11.7 volts, some engineer at Nissan needs a kick in the backside!

11.8 volts on a Lead Acid battery (depending on temperature) is considered to be fully discharged! Here are a couple of references:

Battery voltage and state of charge - Energy Matters

Battery State of Charge using a Voltmeter

Furthermore, letting a standard "starter" Lead Acid battery discharge to below about 50% is extremely bad for it's longevity - even then it will only last a few tens of cycles with a 50% discharge. To keep it from going below even 50% the charger would have to kick in when the rest battery voltage went below 12.2 volts.

So if the Leaf does have a system that kicks in to top up the 12 volt battery when parked and turned off, but it waits until 11.7 volts, it's about as much use as a chocolate teapot! :rolleyes:

And if we have a high vampire drain when the car is off that readily gets it down to this point, there is your Leaf 12 volt battery issue right there. All completely avoidable.
 

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The bit i dont get is all ICE engines continuously "over charge" their lead acid batteries, continually pouring 14v into them regardless of state of charge, and yet they manage to last just fine.

The usual failure i've seen with most of my ICE's is the battery will start the car just fine, but has very little reserve capacity. Sit for 5-10minutes with the cars electronics on and it'll fail to start. So long as you just get in and start it, it'll keep working. But these are batteries which are waay beyond their service life, potentially 8-10 years old.

If the DC converter in an EV acted the same way as an alternator, and just continuously output 14v, then i simply cant see why a standard lead acid gives any problems, despite not being ideal for the use case, the simple fact is the battery should never be drained down as the only time its being used is to keep the electronics alive when the cars off (tens of miliamps and no different to an ICE) and to power up the ECU's for a few moments while the HV side "boots up" and switches on the DC converter, so the fact they dont particularly like deep cycling shouldnt be an issue.
I've mentioned this elsewhere, but the DC/DC inverter in my Ion seems to charge the battery to around 14.2 - 14.4 volts (probably temperature compensated, hence the different readings I've seen at different times) constantly any time the car is either charging the traction battery or the car is "on" ready to drive. When I've checked I've never seen it at 14.2v when "on" or charging from the wall.

I haven't seen any reports of unduly failing Ion/C-Zero batteries! It never charges the 12 volt battery when the car is parked, turned off and not plugged in though. So while the vampire drain seems to be very low, if you did leave it a couple of months it would probably discharge the 12v battery.
 

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Discussion Starter #46
Just checked my Leaf. Battery is down to 12.2v with with everything off. In accs mode it drops to 11.7v. In drive mode it immediately starts charging at 14.3v. Stays around that value for about 10 mins then slowly reduces to 13.1v. Didn't wait around for more to change.

I think the battery is kaput and will replace it with similar. It is unlikely to let me down in the short term since it won't happen on route to anywhere.
 

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Just checked the ampera, 12.5 at rest, didn't do a load test
 

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Just checked my Leaf. Battery is down to 12.2v with with everything off. In accs mode it drops to 11.7v. In drive mode it immediately starts charging at 14.3v. Stays around that value for about 10 mins then slowly reduces to 13.1v. Didn't wait around for more to change.
The voltage levels referenced by the articles I linked to refer to the "at rest" voltage, which is when there is no charging and no load, and it does take a while for the voltage to stabilise at the at rest voltage if the battery has been recently charged, (about an hour I think) due to it taking time for the surface charge to dissipate.

12.2 volts with everything off for at least an hour suggests the battery is only approximately 50% charged.

Dropping from 12.2 volts to 11.7 in ACC mode is pretty poor, unless the ACC mode is turning on a lot of loads like electric seat heaters, headlights and so on. Even then it should should still stay above 12 volts.

Ideally you'd want to see about 12.6 volts for the at rest test a few hours after the battery has been charged, and not dropping below about 12.2 volts with accessory loads.

The battery could be stuffed, but I would tend to put it on an intelligent battery charger first to give it a chance to be properly charged (which the Leaf itself doesn't seem to be able to do!) then repeat the at rest and ACC voltage tests.

If you still get a similarly poor result after the battery has had a proper charge, it needs replacing.

I have this intelligent charger which I think I paid £13 for from Lidl which has been very good:

Produktdetails

I use it on my ICE which sometimes doesn't get driven for 2-3 weeks at a time either left on it to automatically maintain the battery or to charge it up if it has accidentally been left too long to go down.

I used it on my Peugeot Ion once when I accidentally ran the battery down by leaving the car in ACC for about 6 hours with the electric seat covers on. Whoops! :oops: That's the only 12 volt battery problem I've had with it though.
 

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Just checked my Leaf. Battery is down to 12.2v with with everything off. In accs mode it drops to 11.7v. In drive mode it immediately starts charging at 14.3v. Stays around that value for about 10 mins then slowly reduces to 13.1v. Didn't wait around for more to change.

I think the battery is kaput and will replace it with similar. It is unlikely to let me down in the short term since it won't happen on route to anywhere.
I doubt it is bad. It has just had months of undercharging. Get a decent desulphation charger and put it on a 48 hour charge. All will be well, I am confident.
 

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I doubt it is bad. It has just had months of undercharging. Get a decent desulphation charger and put it on a 48 hour charge. All will be well, I am confident.
Technically if it is suffering from sulphation it is currently "bad" and not simply discharged - it won't perform normally after a single "normal" charge due to the high cell resistance. I guess what you mean is that it is potentially recoverable with the right charging/rejuvenation regime.

I'm skeptical that it is sulphated though as that doesn't normally happen until you get below about 11 volts and leave it there for a significant period of time. (days or more) In other words a battery that has been deeply discharged and then left to sit for quite a while, especially if left to sit with a load like headlights left on to pull the voltage down very low.

This is why if a lead acid battery does get deeply discharged to the point where it won't start the car (EV or ICE) it's critical that it is charged up ASAP before significant sulphation gets a chance to develop.

The charger I use that I recommended has an automatic pulse charge desulphation routine, but this runs between 7.5 - 10.5 volts, which is the typical voltage of a battery that has been left to sit discharged long enough to suffer from sulphation.

The diagram below shows its charging routine:

Charging.png


Also rather than a simple constant voltage 13.8 volt float it charges to 14.4 volts, then drops to a very low trickle - once it drops to 12.8 it will charge back to 14.4v again then go back to a trickle. This is better for long term maintenance of the battery than a constant voltage float as it minimises electrode corrosion that occurs at 14.4 volts, but at the same time because it never lets it go below 12.6 volts when at rest it keeps it at 100% SoC.

I'd say the battery in question is not sulphated as it hasn't be discharged to a low enough voltage for long enough, however it seems a bit like the Leaf may fail to do the "absorption" phase adequately to ensure the battery is ever fully charged - as I said earlier I'd put it on an intelligent charger and give it 24 hours and test it again. It may be fine after that.

If it seems fine for a few weeks after that it shows a clear shortcoming in the charging system in the Leaf, in which case I would put it on the intelligent charger once a month for "maintenance" as a workaround to keep the battery healthy.
 

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All this talk of rest state battery voltage got me curious, so I went out to check the battery voltage on my Ion.

It's roughly 4 hours since the car was driven - a relatively short 10 minute drive for groceries. The car was not plugged in to charge after coming back as it's still over 90% SoC.

I measured 12.73 volts at the battery terminals. This is actually a bit higher than I was expecting to see, although it's possible it hasn't rested for long enough to show a true "at rest" voltage. (I might check it again after it has sat overnight)

But in any case, this indicates a fully charged and probably healthy battery.
 

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Most evs seem to have simple cranking style 12v batteries, and that makes sense. A leisure style cell can go very low voltage, but dont seem to like being float / high degree charged, and dont give out large current discharges. They also seem to fail very prematurely. The high discharge rate is important, many power steering systems (especially hydraulic ones) can easily pull 70 amps at full load, and thats often at the limits of the DC to DC converter capabilities, so a simple battery having large current short term capabilities makes sense, as does having one thats large ah capacity. If you have headlights, demister fan, wipers and then turn the steering you can readily pull 100amps, chuck in the sound system and the general EV system demands, and you can see why a decent discharge rate battery with a decent storage ah is vital. Thats not a leisure battery.
A std 12v battery (especially the non watering ones) do put up with a lot of over charge (they simply get hot and gas) You cant do that with a leisure battery, well you can they just dont last long, as is the case when used in a heavy discharge / high charge rate .
The point of over charging a lead acid is to get the internal cells as balanced and therefore holding as much charge as possible. On vehicles like the Polaris Ranger that is made with two strings of 4 x 12v batteries, the original algorithm of the charger causes heavy overcharge and gassing, but the ranger also has a 12v tap off the first battery in each string, so over charging ensures that that battery gets fully charged. They also have a watering system, and if done regularly the cells hold up well.
I have seen EV conversions where people have put a shed load of money into a Optima round cell unit, great discharge rate, but actually a very low ah capacity for the format size. So actually overall not a good choice.
A good ah, good discharge rate 12v battery is vital with an EV, use what the makers recommended (type etc) as that will work best with the operation sequence and peak charge rate of the DC to DC, change to something else and you run the risk of over charge, under charge, over heat, etc etc. Yes its almost a service item, and not much more costly than an Aircon regas at a main dealer. (And why regas regularly, as that suggests a leak)
 

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Discussion Starter #54
I'm skeptical that it is sulphated though as that doesn't normally happen until you get below about 11 volts and leave it there for a significant period of time. (days or more) In other words a battery that has been deeply discharged and then left to sit for quite a while, especially if left to sit with a load like headlights left on to pull the voltage down very low.
It has been parked for a couple of days.

My charger is a slow/fast charger, top is about 5.6 amps. It is a few years old. Was used to keep the fence batteries charged.
 

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The point of over charging a lead acid is to get the internal cells as balanced and therefore holding as much charge as possible. On vehicles like the Polaris Ranger that is made with two strings of 4 x 12v batteries, the original algorithm of the charger causes heavy overcharge and gassing, but the ranger also has a 12v tap off the first battery in each string, so over charging ensures that that battery gets fully charged. They also have a watering system, and if done regularly the cells hold up well.
The point about balancing the cells via controlled "overcharging" is a very good one. Something I'm aware of but didn't mention.

Lithium Ion cells don't tolerate any overcharging at all and even if you did overcharge them the cells would still not be balanced as the overcharge energy would still actually be stored and returned later. (At the expense of risk of fire, short cycle life etc) So Lithium Ion needs active cell balancing technology.

Lead Acid on the other hand does tolerate a lot of overcharging, once fully charged the cells just gas and generate heat with the "excess" energy, but don't store any more energy. As long as the overcharging is at a modest rate there is no risk of damage.

So any cells that reach full charge before others just gas and generate heat while the laggards catch up. At the end of it the cells are balanced and all at 100% SoC.

Without that controlled overcharging (14.4 volts) the cells would get out of balance and the usable capacity of the battery could drop significantly or even result in individual cells sulphating during deep discharge due to individual cells being at a lower voltage and SOC than others.

So if the charging system in the car doesn't put the battery through a proper charging regime on a regular basis which includes a full absorption phase that gives time for all the cells to balance the battery will suffer in the long term.
 

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it's a pity not all EVs have a 12V battery voltage display.
this would indicate to users that their 12V was either not being charged or about to die ?
(i appreciate the V alone does not indicate capacity, but it helps)
 

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It strikes me that Nissan, not only use the wrong traction battery , but have equal contempt for buyers regarding the 12v battery...
 

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From my readings of many other posts on this forum, and a little testing and experimentation on our Leaf, I belong to the camp that believes that the discharged 12V battery in pre 40 kWh Leafs (and maybe other EVs too) is often due to a certain state that the car gets in, that discharges the 12V battery without invoking the DC-DC converter to recharge. I don't know what precisely the state is that triggers the discharge, but I think it may have to do with neutral, locker/unlocked car, off but still on.

Maybe it is quite a small camp.
 

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I measured 12.73 volts at the battery terminals. This is actually a bit higher than I was expecting to see, although it's possible it hasn't rested for long enough to show a true "at rest" voltage. (I might check it again after it has sat overnight)
I checked again after the car has sat unused over night and it's still 12.73 volts.

Interesting thing is that I had to use the central locking to open the doors to get to the bonnet pull - when I initially measured the voltage it was down to 12.6 volts exactly, however over about 2 minutes it crept back up to 12.73 again. This is due to the load of the central locking unlocking the doors and the wing mirror extension - even though they don't last long.

Lead Acid batteries do have this very delayed elastic effect, hence why they have to sit quite a while before measuring rest voltage.

Even a temporary discharge just before taking the measurement like central locking activation will temporary depress the voltage reading, so leaving the bonnet popped over night is probably the best way to get an accurate reading in the morning without activating any systems like central locking to discharge the battery.
 

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My Gen1 leaf has a high at rest current draw. The randomness of my phantom battery drain problem suggests this draw is intermittent. So far I have eliminated the possibility of a wiring fault or anything I have installed. To my mind this only leaves a software bug of some sort that I won't be able to fix, so the cure for me is either a higher capacity 12v of whatever design, don't leave the car standing for several days, or fit a disconnect on the live terminal.

I don't think that draining the battery does knacker it for an ev like it does for an ice, due to the fact the high requirement for a high crank amperage is not needed.
 
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