Nissan Leaf 12 V battery troubles have been avoided, but if they happen, would a jump pack be useful?

Forums › Transport (cars, bikes and boats) › Nissan Leaf 12 V battery troubles have been avoided, but if they happen, would a jump pack be useful?

jlittle

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#322792 23-Sep-2025 06:44

After advice on the general Leaf thread, I hook up the 12 V battery to a charger every 6 weeks or so, and haven't had trouble since.

However, it's occurred to me that I have a little Jaycar jump starter. (It had no trouble cranking the V6 in my Holden). Would it be useful if a Leaf gave 12 V battery trouble?

Regards, John Little

Stu

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#3417585 23-Sep-2025 07:01

Unless the Leaf has some weird stuff going on, it should be all good. I carry a small Noco jump pack in our Niro. Just in case. Doesn't need much to get it going.

People often mistake me for an adult because of my age.

Keep calm, and carry on posting.

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Jase2985

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#3417934 23-Sep-2025 15:09

I highly recommend removing the small current sense plug off the negative battery terminal. This allows the leaf to charge the battery at 14.0x volts, as opposed to the default 13.0x volts. This makes a huge difference, as lead acid (name your variant) like higher charging voltages.

I would constantly see the state of charge of the battery in the 50%'s (battery is only 5 months old at the time) with its voltage as low as 12.2 volts after driving with the plug connected. I invested in a bluetooth battery monitor to keep an eye on the battery voltages after i got home from work one day and the battery was flat not long after i had just turned the car off from a 30 minute drive. research showed disconneting the plug helps and there are next to no downsides.

The charging system does charge the 12v battery when charging via AC/DC, and it picks and chooses when to charge when driving but it uses the lower voltage which isnt enough for the battery. Removing the plug allows a higher voltage charge when charging via AC/DC and when the car is in ready to drive/drive mode.

fastbike

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#3418619 25-Sep-2025 06:59

Jase2985:

I highly recommend removing the small current sense plug off the negative battery terminal. This allows the leaf to charge the battery at 14.0x volts, as opposed to the default 13.0x volts. This makes a huge difference, as lead acid (name your variant) like higher charging voltages.

Or briefly turn the heatpump on, then off when you start the car - that is enough to trigger the DC-DC charger in the car to top up the 12V battery from the traction battery.

I'm running OVMS so can monitor the 12V battery actual state and have an alarm set if it drops below 11.5V

Otautahi Christchurch

Jase2985

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#3418681 25-Sep-2025 09:15

fastbike:

Jase2985:

I highly recommend removing the small current sense plug off the negative battery terminal. This allows the leaf to charge the battery at 14.0x volts, as opposed to the default 13.0x volts. This makes a huge difference, as lead acid (name your variant) like higher charging voltages.

Or briefly turn the heatpump on, then off when you start the car - that is enough to trigger the DC-DC charger in the car to top up the 12V battery from the traction battery.

I'm running OVMS so can monitor the 12V battery actual state and have an alarm set if it drops below 11.5V

Even then, it does a poor job of topping it up. Removing the charge sense plug means you don't need to worry about anything and the battery gets charged all the time at a decent voltage like it would in an ICE vehicle.

And 11.5v yuck, a 12v batteries shelf state should be 12.4-12.7v, going that low, 11.5v, is not good for it.

ezbee

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#3418695 25-Sep-2025 10:14

On a side note,
Its stunning that a major car company seems to have lost the most basic knowledge on how to care and feed millennium old lead battery.

I'd love to know what is going on inside the design process.
Its so far in the 'not hard at all' , 'done it countless times before' territory.

Jase2985

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#3418699 25-Sep-2025 10:40

ezbee:

On a side note,
Its stunning that a major car company seems to have lost the most basic knowledge on how to care and feed millennium old lead battery.

I'd love to know what is going on inside the design process.
Its so far in the 'not hard at all' , 'done it countless times before' territory.

yep, it's pretty bad. About 75% of all leaf issues can be traced back to a low or faulty 12v battery.

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richms

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#3418713 25-Sep-2025 12:07

ezbee:

On a side note,
Its stunning that a major car company seems to have lost the most basic knowledge on how to care and feed millennium old lead battery.

I'd love to know what is going on inside the design process.
Its so far in the 'not hard at all' , 'done it countless times before' territory.

They only care about efficiancy. Putting more than is needed into a SLA makes it heat up, wasting energy.

Look at all the smart chargings BS that some ICE cars and vans come with which make the voltage swing all over the place depending on what it thinks you need. All that for a tiny improvement in the numbers.

Richard rich.ms

tripper1000

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#3418736 25-Sep-2025 15:38

Yes, 12v jump pack saved me multiple times when my Leaf 12v system was giving trouble. The owners manual shows you how to jump start the car with jumper leads, so an auxiliary 12v starting source is permitted by Nissan.

I also recommend a 10mm spanner in order to clear the random warning lights by disconnect negative battery lead momentarily. Various ECU's can log erroneous faults when the 12v battery drains below 9 volts.

If the dash is lit-up with error lights after you get the car "started", let the car "run" for a couple of minutes so the 12v battery recovers somewhat, turn car off, disconnect negative for 30 seconds, reconnect and bob's your uncle. Alternatively, if you have it, you can also use Leaf Spy to clear DTC's, but if you have any more than 4 or 5 ECU faults to clear, it can be quicker to do the battery thing.

If you're not getting error lights, you don't need to disconnect the battery.

It only needs a modest jump pack - the Leaf requires a lot less starting current than a ICE. My jump pack was still starting the Leaf when it was too worn to start a ICE.