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Discussion Starter · #1 ·
Nicely hoist on my own petard today - stranded due to running out of 12V battery. I replaced it about 2 years ago, and thought 'all those 12V issues won't be a problem for me for a while...'. How wrong was i ? Very. I'd left the car with the hazards on for about 90 minutes or so (yes, it was a proper hazard) and got in, turned on and was greeted by warning light extravaganza on the dash - but no starting or 'green car' logo. After some severe self-chastisement (particularly the being too cheap to have joined the AA/RAC/GreenFlag; sigh), i pondered my options, and was fortunate enough to be close to a Halfords. So, i picked up one of those pocket sized battery jumpers as i figured even something puny should be able to start a Leaf (given it seems that the 12V is nearly as powerful as a AAA battery). First go with the booster didn't work - still a mess of lights. Then i unplugged the 12V for a few seconds, and second time it fired up just fine.

Once going, i returned to Halfords and bought a smart charger, as i guessed it would be prudent. So, my question; being old, i disconnect the battery terminals before charging - but, is this required on the Leaf ? Also, how infrequently can i get away with charging the 12V ? i'm hoping maybe every 6 months - or is this too little ?
 

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Official advice is to disconnect the 12v DC before connecting the charger. That goes back to ancient lead acid tech where there was a risk of H2 being produced at the battery and a spark being made when connecting could cause an explosion. Anyone ever hear of that actually happening - ever ? More recently the fear was that some modern cars have a sensor on the pos terminal that sends info to the ECU and if it suddenly detects 14v there it could cause a malfunction needing a dealer visit to reset. In practice I have been leaving the battery connected for years with no issues when attaching a charger.

If you search the forum for such issues you will find dozens of threads and over the years I have always recommended the regular use of a smart charger whether the car seems to need it or not. The main point is to not only charge the 12v DC, but to condition it, as that is the main benefit of a smart charger over a dumb unit.

Look on it as a preventative monthly maintenance item alongside the tyre kicking, screenwash filling and wiper blade cleaning. I actually put mine on twice a month when the car is likely to be stood for some time. Sometimes overnight. And I use a phone reminder for that. It also should be left connected as long as it takes to report that it has completed its process. Sometimes that can be many hours at 0.2 amps but that is still needed as it could be repairing any sulphidation issues.

It's a feature of EV life that is annoying but avoids events such as you experienced. Some people rant and rave that this shouldn't be necessary. And they are right. But life is too short to become all bent out of shape about this when a tiny amount of regular action solves it long term. In your case, this probably killed your first 12v battery and was well on the way to trashing the second one. Your smart charger should repair any damage and prevent it from happening again.
 

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As above. Early LEAFs such as yours don't protect the 12v as well as later versions which is of no help to you but means that the experience of the owners of later cars is irrelevant. It's well worth using a good quality battery conditioner once a month and your 12v will be in better condition because of it.
But, even ICE 12v batteries in good condition will go flat after 90 minutes of hazard lights. FWIW my previous E61 BMW's battery started the 3 litre diesel reliably even in cold weather but using the radio for 60 minutes with the engine off was enough to flatten the battery to the point of needing a bump start on two occasions - thank goodness for manual transmission. Emergency services vehicles leave their engines running when standing but lit to avoid similar problems.
 

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Discussion Starter · #5 ·
Official advice is to disconnect the 12v DC before connecting the charger. That goes back to ancient lead acid tech where there was a risk of H2 being produced at the battery and a spark being made when connecting could cause an explosion. Anyone ever hear of that actually happening - ever ? More recently the fear was that some modern cars have a sensor on the pos terminal that sends info to the ECU and if it suddenly detects 14v there it could cause a malfunction needing a dealer visit to reset. In practice I have been leaving the battery connected for years with no issues when attaching a charger.

If you search the forum for such issues you will find dozens of threads and over the years I have always recommended the regular use of a smart charger whether the car seems to need it or not. The main point is to not only charge the 12v DC, but to condition it, as that is the main benefit of a smart charger over a dumb unit.

Look on it as a preventative monthly maintenance item alongside the tyre kicking, screenwash filling and wiper blade cleaning. I actually put mine on twice a month when the car is likely to be stood for some time. Sometimes overnight. And I use a phone reminder for that. It also should be left connected as long as it takes to report that it has completed its process. Sometimes that can be many hours at 0.2 amps but that is still needed as it could be repairing any sulphidation issues.

It's a feature of EV life that is annoying but avoids events such as you experienced. Some people rant and rave that this shouldn't be necessary. And they are right. But life is too short to become all bent out of shape about this when a tiny amount of regular action solves it long term. In your case, this probably killed your first 12v battery and was well on the way to trashing the second one. Your smart charger should repair any damage and prevent it from happening again.
Thanks. I was following the 'disconnect rule' - though didn't know why. I was also a bit concerned about charging these new batteries that don't have unscrewable cell covers, which were used to top up the electrolyte. I'm guessing they've some kind of vent, or produce less H2. Yep, i'm that old...

I'll leave it connected and save myself needing to reset the clock every time. Of course, now there's the powerbank thingy in the glovebox (also better for charging phone than the puny USB in the car) i'm sure that i'll find myself with dead 12v again at some point - being too lazy to follow a 12v charging and conditioning routine. After a few strandings, i may overcome the inertia :)
 

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Discussion Starter · #6 ·
As above. Early LEAFs such as yours don't protect the 12v as well as later versions which is of no help to you but means that the experience of the owners of later cars is irrelevant. It's well worth using a good quality battery conditioner once a month and your 12v will be in better condition because of it.
But, even ICE 12v batteries in good condition will go flat after 90 minutes of hazard lights. FWIW my previous E61 BMW's battery started the 3 litre diesel reliably even in cold weather but using the radio for 60 minutes with the engine off was enough to flatten the battery to the point of needing a bump start on two occasions - thank goodness for manual transmission. Emergency services vehicles leave their engines running when standing but lit to avoid similar problems.
Ah, it seems i've woefully over-estimated the ooomph in the 12v. Will make a note to myself not to get stuck on a motorway or somewhere really tricky (eg NC500) where the cavalry might take a while to arrive. Of course, i'm feeling the irony of having 40kWh of juice underneath the car, but not enough in the 12V. Sigh.
 

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Battery explosions? Yes, they do happen. I was a HGV fitter with my county fire service for many years, at our workshop we had a battery charging shop, one morning a colleague went to disconnect a battery left charging overnight, he omitted to switch off the charger at the mains, simply pulled off the clips, there was a loud bang and he was showered with dilute sulphuric acid. Luckily he wasn't badly hurt and mercifully no acid went into his eyes, even though he wasn't wearing eye protection, So yes, the risk is very small, but it's still there.
 

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Discussion Starter · #8 ·
Official advice is to disconnect the 12v DC before connecting the charger. That goes back to ancient lead acid tech where there was a risk of H2 being produced at the battery and a spark being made when connecting could cause an explosion. Anyone ever hear of that actually happening - ever ? More recently the fear was that some modern cars have a sensor on the pos terminal that sends info to the ECU and if it suddenly detects 14v there it could cause a malfunction needing a dealer visit to reset. In practice I have been leaving the battery connected for years with no issues when attaching a charger.

If you search the forum for such issues you will find dozens of threads and over the years I have always recommended the regular use of a smart charger whether the car seems to need it or not. The main point is to not only charge the 12v DC, but to condition it, as that is the main benefit of a smart charger over a dumb unit.

Look on it as a preventative monthly maintenance item alongside the tyre kicking, screenwash filling and wiper blade cleaning. I actually put mine on twice a month when the car is likely to be stood for some time. Sometimes overnight. And I use a phone reminder for that. It also should be left connected as long as it takes to report that it has completed its process. Sometimes that can be many hours at 0.2 amps but that is still needed as it could be repairing any sulphidation issues.

It's a feature of EV life that is annoying but avoids events such as you experienced. Some people rant and rave that this shouldn't be necessary. And they are right. But life is too short to become all bent out of shape about this when a tiny amount of regular action solves it long term. In your case, this probably killed your first 12v battery and was well on the way to trashing the second one. Your smart charger should repair any damage and prevent it from happening again.
I've a further question - can i have the car plugged in and charging via Type2/type1 and charge the 12V at the same time? (while still connected).

I'm thinking this wouldn't work, as main battery charging may need to access some current from the 12V to run the BMS/CAN bridge etc ? This wouldn't react well to some extra amps from the charger (?).
 

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Battery explosions? Yes, they do happen. I was a HGV fitter with my county fire service for many years, at our workshop we had a battery charging shop, one morning a colleague went to disconnect a battery left charging overnight, he omitted to switch off the charger at the mains, simply pulled off the clips, there was a loud bang and he was showered with dilute sulphuric acid. Luckily he wasn't badly hurt and mercifully no acid went into his eyes, even though he wasn't wearing eye protection, So yes, the risk is very small, but it's still there.
That is where the 'best advice' comes from of course. Old style batteries with liquid acid and powerful dumb chargers that just kept pouring amps into them even when they were full. It sounds like that had been left overcharging all night and perhaps that was the mistake, together with failing to disconnect before tampering with the clips. I have always surmised that such overcharging could be the cause of such events as perhaps the acid became too warm/hot and emitted a lot of H2.

The old disconnect advice went as far as to actually remove the battery from the car to avoid such an event torching the car. If you think about that reported event the problem wasn't that it was connected - just that there was a lot of H2 there waiting for a spark. And that would have happened whether the truck terminals were connected or not. And also have happened if the batteries had been removed and were sat on a workbench. Recognising this, I have always only energised the charger once the croc clips were attached and always switched it off before detaching them to avoid any spark possibility.

I've a further question - can i have the car plugged in and charging via Type2/type1 and charge the 12V at the same time? (while still connected).
I have done that quite a few times without incident. The manufacturers will have designed the main charging system with diodes and safety devices to isolate them from each other. If it was an issue there would be severe warnings about that in all manuals. But there aren't. So I take it that it is yet another problem perceived rather than real.
 

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Does the car not already run the 12v DC-DC system while charging the traction battery? I'd be surprised if it didnt, given its running the coolant pump/fans/battery contactors etc all from the 12v system...
 

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Does the car not already run the 12v DC-DC system while charging the traction battery? I'd be surprised if it didnt, given its running the coolant pump/fans/battery contactors etc all from the 12v system...
Could be. But again, that is just a low charge like a dumb unit. A smart charger does much more. It analyses the condition of the 12v battery and based on that result goes on to run a set of programmes to correct any issues discovered. That can involve a change in power delivered over time and some even pulse charge to drive off any dendrite build up as well as rectify any other sulphidation problems detected. The use of a smart charger regularly is much more than a simple battery top-up that we have all grown up to understand. A healthy battery will then hold a full charge longer and avoid the many problems being discussed.
 

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Discussion Starter · #12 ·
That is where the 'best advice' comes from of course. Old style batteries with liquid acid and powerful dumb chargers that just kept pouring amps into them even when they were full. It sounds like that had been left overcharging all night and perhaps that was the mistake, together with failing to disconnect before tampering with the clips. I have always surmised that such overcharging could be the cause of such events as perhaps the acid became too warm/hot and emitted a lot of H2.

The old disconnect advice went as far as to actually remove the battery from the car to avoid such an event torching the car. If you think about that reported event the problem wasn't that it was connected - just that there was a lot of H2 there waiting for a spark. And that would have happened whether the truck terminals were connected or not. And also have happened if the batteries had been removed and were sat on a workbench. Recognising this, I have always only energised the charger once the croc clips were attached and always switched it off before detaching them to avoid any spark possibility.



I have done that quite a few times without incident. The manufacturers will have designed the main charging system with diodes and safety devices to isolate them from each other. If it was an issue there would be severe warnings about that in all manuals. But there aren't. So I take it that it is yet another problem perceived rather than real.
Thanks - this will considerably increase the likelihood of 12V maintenance, as i'll charge both batteries overnight together. I have my type2 inside my garage, and there's a handy 240v socket (for granny charger or my new smart 12V charger). I'm a very lucky boy - detached double garage (it's a newbuild), with home-built workbench.
 

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Could be. But again, that is just a low charge like a dumb unit. A smart charger does much more. It analyses the condition of the 12v battery and based on that result goes on to run a set of programmes to correct any issues discovered. That can involve a change in power delivered over time and some even pulse charge to drive off any dendrite build up as well as rectify any other sulphidation problems detected. The use of a smart charger regularly is much more than a simple battery top-up that we have all grown up to understand. A healthy battery will then hold a full charge longer and avoid the many problems being discussed.
Sure, but is it going to be able to do all of that smart stuff while the cars running a DC-DC converter at the same time? I would imagine such smart features requires careful monitoring of the battery voltages and charge parameters. Connected into a circuit with a big DC converter running a bunch of fans/pumps/electronics i doubt is going to work very well. If its anything like mine, it'll either just declare the battery is full, or will decide theres a fault.

The reality is a decent saturation charge to 14.4v is enough to keep most batteries healthy. Thats what the "dumb" alternator in ICE cars has done for 50 years, and it works remarkably well. The touted smart features i feel are 90% marketing. Yes, they might work in some cases, but they generally arent required.

The main issue the LEAF has, is it deliberately doesnt run its DC to DC at 14.4v, as running a lower voltage means less energy is wasted in charging the 12v. Mine for instance will run at 14.4v for some period of time after starting the car, before dropping down to 12.8v. At 12.8v the voltage is low enough that the 12v battery isnt actually charging at all. The DC converter modulates its output to try to maintain a 0A discharge from the battery.

The issue seems to be that the time it runs at the higher voltage for, is not long enough to actually recharge the battery, and so over time it ends up running lower and lower. Eventually this causes the battery to physically deteriorate from being run for a long time at a low SOC.

I've charged my LEAF battery once. Which was a preventative measure last June after the car had sat for ages and hadnt been used much.
 

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The issue seems to be that the time it runs at the higher voltage for, is not long enough to actually recharge the battery, and so over time it ends up running lower and lower. Eventually this causes the battery to physically deteriorate from being run for a long time at a low SOC.
You have just explained precisely why a smart charger is required. Absent the smart features, to condition and repair the damage you have described, the battery will eventually die. This isn't about charging a flat battery. It's about repairing damage caused by it being continuously flat.

A decent smart charger does that and then goes on to float charge. My early Leaf 24 had two episodes of bizarre electrical incidents and one lock-out with the 12v battery changed under warranty between these events, A forum member with a deep understanding of lead/acid tech advised me to buy a smart charger and apply it monthly. The car 12v system ran flawlessly for the next three years. And this Ioniq has also been 12v issues free.

I realise that the use of a charger regularly is a pain. I know it should not be necessary. I understand the resistance. But as I said, life is too short to stress over such a simple remedy that involves a minute to connect and disconnect 12 times a year.
 

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Yeah, i was more pointing out that trying to "smart" charge while the car is also actively driving the 12v circuit isnt likely to work as expected. How can it possibly analyse a battery, in a circuit with not only various active loads, but also another power supply driving it...

A totally standard charger applied monthly will do the job just fine, it doesnt have to be anything particularly special, so long as the battery isnt wrecked.
 
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