Replace old cell with new cell

[rsbrax]

Good info in responses. My intention is to keep the 2012 Leaf with expectation of 8 years useful life remaining. It is in near mint condition with only 35k miles and custom leather interior installed when I purchased new. The license tags were removed in 2022 after I purchased a new Audi e-tron Quattro. I want to use the Leaf for local driving and not worry about having to re-charge daily. The range is about 35 miles on an 80% charge. Other than degradation the 24kWh pack seems good according to LeafSpy; no bad cells.

 

[Ingbert]

The question really is: at what point does the weak cell impact your driving/safety? Weak/bad cell problems typically manifest themselves at low SOC, and how low depends on the magnitude of the voltage delta. I noticed problems once I got beyond a 100mv delta, so I can't imagine driving the car with a 200-300mV delta. Of course, that assumes you even can/want to make the repair; it's not cheap, and you definitely don't want to do it twice...so make sure you have identified all the problem modules (there are 8 cells/module in the 40kWh and 62kWh packs).

Thanks for information. I do a deltacheck twice a year at SOC 50%. My readings are 25 mV or lower.
I have a 2018 model Tekna 40000 Km. Not an issue yet. Live in south Sweden.

 

[k9spud]

The problem is heat-transfer. If there is only air around the cells, it will effectively act as an insulator.

Air is not too bad for removing heat, IF the air is moving. But the Leaf battery is encased in a partially vacuum sealed metal case, so there isn't much air in there and it's not moving. So yes, effectively an insulator.

Of course you can use cylindrical batteries - Tesla has been doing that for a long time - but those serpentine cooling coils they use for dissipating the heat are probably out of the question for DIY type battery making.

I don't have a link handy, but there exists a youtube video of Lucid Motors CEO showing off how they cool their cylindrical batteries. The cute thing they did was attach both the positive and negative battery conductors to only one end of the cylindrical battery (the end typically used as a positive terminal). They mount the cylinder upside down so that heat can flow upwards to the flat negative end of the cylinder. Using that flat surface, they can then use an aluminum plate with internal fluid channels to act as a heat sync.