Nissan Specialist told me Leaf has replacable battery modules..

Analogous to a chain, a series battery pack typically fails at its weakest member. As years pass, the Leaf owner will notice a loss of capacity, but the weakest cell will likely give out before the pack as a whole reaches end of life. That should provide some comfort, to know that, after warranty expires, a battery problem might be fixed at moderate cost, rather than replacing the whole pack.

The Prius traction battery is similar. In the absence of chronic overheating (clogged battery fan), it is usually a random cell out of the 168 that fails. JeffD's battery is a classic case, where 1 cell in 1 module was bad, but he was able to recondition the others back to full capacity. If you talk to Toyota, you have to buy another battery, but if you talk to someone else, a simpler/cheaper fix is usually possible.

 

In the Service & Maintenance Guide guide for the Leaf, downloadable from Nissan Owners | Manuals & Guides | Nissan USA, there's a Li-ion BATTERY REPLACEMENT RECORD section where info is supposed to be recorded if a module or the whole assembly is replaced.

 

i agree that Nissan will most likely come up with a prorated replacement policy on module replacement. with the 24 modules (each with 4 cells) we are talking a battery pack voltage just over 400 volts. to insure longevity charge voltage is set to just over 4.17 volts (cellphone batts charge to 4.21-.24 volts greatly reducing lifespan but done so due to additional talk time and relatively low replacement costs) making a pack voltage of about 402 volts.

when one module fails and power is applied it acts like a weak link in a chain which could drop the voltage of the module to under 10 volts from 16.68 volts. this can make a pack that is charged to 95+% act as a pack charged to under 80%. two modules failing drops pack voltage even farther.

i am getting a "GID SOC" meter next month (yes, Xmas Present to myself!!) so will have more details but i experienced the same issues with my Zenn. batteries may run at 13.8 volts and i put power to it and 10 miles later, 4 batteries would be at 12.5 volts under load and the bad ones would be at 10.5

so battery packs work the weakest cells the hardest. so replacing a single module could increase effective range 10+ % despite replacing only 4% of the pack capacity.

Nissan definitely did this right and i am guessing their battery plant will produce these modules at a pretty low cost/unit price

many have wondered how dealerships will replace their "nest egg" aka as ICE maintenance when EVs get more popular. guessing replacing these modules in a very well protected battery pack enclosement will fetch a pretty hefty labor tag

 

The Leaf never goes above 394.5V on it's battery pack so your 4.17V per cell is wrong. Max voltage per cell is about 4.11V.

 

"guessing replacing these modules in a very well protected battery pack enclosement will fetch a pretty hefty labor tag"

That *is* the question. How much is the labor going to be. If the LEAF becomes popular enough independents like Seilerts might save the day.

 

While modular replacement adds flexibility, and flexibility is always a good thing, I'm not sure dropping one new module into an older used battery is a good idea, because now the good (new) module will be dragged down by the older (no longer like-new) modules.

Where modular replacement has real potential is in the case of an early failure of one module. A new one is then not overly out of line with the rest of the pack.

A likely aging scenario is that after some years, the modules will have slightly differing capacities remaining, and replacing the worst one will make only slight improvement. Replacing the next worse one will have another slight improvement. And so on. You'll have to replace a lot of them to have a significant improvement, and the ones you don't replace will be nearing their end of life.

Modular design will benefit the manufacturer as regards warranty work in case of early failures due to defects, more than it benefits the owner facing the effects of normal long-term aging.

Modular design probably also makes the manufacturing process simpler. And it might make monitoring and battery management simpler. In an appropriately designed car, the BMS could take an entire weak module off line, reducing power and range, but protecting the pack.

 

I like the fact that one can replace modules of the traction battery as they wear, it makes ownership on my part much less uncertain, before this became apparent I was trying to decide when to sell my prius, now I'm rather interested in seeing how many years I can get out of it.

 

this is the #1 no-no for Lead Acid batteries. effective pack management along with charge balancing will eliminate this issue. how effective Nissan's system is is anyone's guess at this point but they do seem pretty confident but only time will tell.

they could have rushed the current Leaf out to the market with the idea of being first (it has worked well so far) hoping to get the TN Battery plant up to speed just about the time the current technology starts to fail with plans of simply providing warranty replacements relatively cheaply while getting Battery Tech 2 to market.

has anyone read up on PolyPlus??? Time thinks they have something good going

 

Per Nissan's First Responders Guide for the Leaf, the fully charged battery voltage is 403.2 volts, with Automotive Energy Supply Corporation (AES) stating that the nominal voltage is 360 volts.

Now, that would reflect a cell voltage of 4.2, so read into that whatever you would like...

 

I'm not so certain. Balancing and pack management can prevent a weak cell or module from causing damage to the rest of the pack, but your range will still be limited by the capacity of the weakest cell. Unless you envision a system that can cut a weak module out of the circuit entirely. But this will lower pack voltage. I can picture a pack with differing capacities in the different modules starting out at full voltage, and by the time it's gone half the original range, so many modules have been cut out of the circuit that the car now accelerates in double the time it takes when fully charged. If your Leaf does zero to sixty in ten seconds when charged, it takes twenty seconds after 45 miles of driving.

Pack modularity is a great way to lower the cost of repair of a defective but still new pack. And it would allow a defective module to be replaced at any time, by finding a module of similar age, to be balanced with the rest of the pack. But it is not (IMO) a solution for gradually replacing modules as they degrade at different rates with age.

 

Is a good idea for prematurely failing modules, but the pack capacity itself won't really be assisted as it ages other than by replacing them all or somehow reconditioning it.

 

I never suggested that a failed module be replaced with a NEW one. As these cars get wrecked, there will be a supply of used modules -- Nissan would be smart to purchase all cars determined to be total loss in order to maintain control over the supply as well as have it be readily available for warranty replacement or resale. To first order, a used module from a wreck is an ideal replacement for a failed module in another car with similar mileage.

 

+1

First - several electrical engineers that are quite knowledgeable on the Leaf have queried the so called "Leaf Specialist" at auto shows. Long story short - they're not. Packing in a new cel or module among weak ones simply puts a bigger strain on the higher voltage cel/module. If even an EV dork like me (when it comes to traction pack maintenance / leveling / monitoring) knows this, then the self proclaimed 'specialist' is just that. I've asked a few of these folks questions that tend to cause their eyes to glaze over ... and that just shouldn't happen if someone is even worth half their electronic salt. Maybe what this person meant was that (ALL THE) modules can be replaced, years down the road. I wana give the fellow as much credit as possible.

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well all this voltage thing will be settled in less than a week. will be building Gary's SOC meter and will have voltage measurements (total pack only) that will correlate with an SOC reading as well. should be fun. will have to hypermile it there. charge up 3-4 hours just to make it back so will be getting to a charging station a few miles from the place we will be assembling them and riding over. estimated time to assemble, BS, etc, should be about 3 hours which will just enough charge regained to make it home. to think of the sacrifice i make while "patiently" waiting for QC to come along!!