Battery Management System

If we're talking OEM Dell laptop batteries, that's another story. Maybe they just have lousy BMS - and maybe it's intentional so we have to buy replacement batteries more often, LOL. Hopefully (and likely) Nissan has gone to great lengths to optimize their BMS for the Leaf.

The component that most affects the battery pack useful life is not the charger, the motor drive controller, or the regen control, but the Battery (cell) Management System.
This "BMS" should really be called "CPS" - Cell Protection System.

just to venture an educated guess, but Nissan has 17 years of Lithium experience, I am betting they have this worked out, just a hunch

Nissan may have enough confidence in their battery chemistry, pack design, and Battery Cell Management System, but how will they "transfer" or "share" that confidence with new (and potential) owners.

Hopefully more than the "Trust us, we're from the Government" type of "assurance".

Perhaps their "Battery Warranty" will be their "assurance"?

Personally, more details of what is being done to "protect" each of the battery cells would help me form a basis for confidence.

How is cell overcharging managed?
How is cell over-discharging detected, and what is done about it?

Each user of a new technology should not have to "experiment" with their own vehicle to find the limits of safe operation.

garygid said:

Nissan may have enough confidence in their battery chemistry, pack design, and Battery Cell Management System, but how will they "transfer" or "share" that confidence with new (and potential) owners.

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There have been rumors that Nissan will be offering a 10 year warranty on their battery. I'm a little skeptical that this will actually happen, but if it does I think that will transfer/share that confidence with new owners. For me, if Nissan is going to cover the battery for 10 years (again, rumor, I can't stress that enough) then that's all I need to know - I don't care how they do it :-D

10 year battery warranty and 80% remaining capacity at 10 years would be huge. It would assuage a couple of my fears right from the get-go.

I think that's the problem I have with the commitment we're being asked to make at the moment - we have to take a lot on faith! It's really time for Nissan to start announcing some specifics.

I agree, more info would help build confidence.

Have a good (and safe) trip to Big Bear today.

I would not be surprised if its pro-rated.

garygid said:

I agree, more info would help build confidence.

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That is true with people like us - but for general public, the confidence comes with longer warranty - may be showing crash test videos etc.

A "good" battery pack will gradually "age", that is normal.

A mid-life battery pack gone "bad" will usually have only a few bad cells (or modules of 4 cells each) that need replacing.

The battery's Cell Management System should be able to "warn" of cells that are getting "weaker", and thus reducing the usable power of the whole pack.

It is not clear at what point the cell (or module) will be declared "bad enough" to require warranty replacement.

How much battery "health" status information will be available to us?

Probably nothing more than the EV equivalent of a check engine light will be available to us.

I'm sure they won't ever replace cells, probably only modules.

in most of the online articles that talk about the battery pack, 5 years is being bandied about, as the possible warranty. Don't know where this 10 year figure has come from. that is a requirement in California for Hybrid batteries, as they are part of the "emmisions" system, no requirement exists for EVs. The Volt will also fall into this 10 year pack warranty, because it is really just a series hybrid (that can be plugged in), which is also why GM is only using %50 of the battery packs capacity, to insure the 10 year life.

garygid said:

I agree, more info would help build confidence.

Have a good (and safe) trip to Big Bear today.

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I just sent you a PM....we're not going. The wife hit some debris on the freeway last night, so I need to go get her two new tires and an alignment instead. Fortunately, I always buy Road Hazard protection, so all I'll be out is the cost of the alignment (hopefully!).

The LEAF's computers have enough information (date, miles) to be able to know when the warranty period is over.

Might the software wait until the warranty has expired before letting us know that one cell (in one module) is "getting weak"?

There are usually early-warning signs that a cell is becoming the "weak link" in the serial chain of cells.

Are we not allowed to know such information?

Bicster said:

Probably nothing more than the EV equivalent of a check engine light will be available to us.

I'm sure they won't ever replace cells, probably only modules.

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You might eventually have independents that will troubleshoot packs to the cell level, and maybe supply exchange packs rather than working on your own and reinstalling it.

10 years of battery warranty would be awesome, but even a 5 year would be OK with me - I'll have somewhere between 60,000 and 75,000 miles on my car by then.

Mitch....I think Mark Perry talks about expecting the pack to last 10 years in that video I posted. Admittedly, this doesn't translate to us being offered a warranty, and it probably shouldn't even raise our expectations about pack longevity without more information.

mitch672 said:

Don't know where this 10 year figure has come from.

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Well, again, I tried to emphasize that this is a rumor, not fact. The last place I saw a mention of a 10 year warranty was mgrigs' post on this page: http://www.mynissanleaf.com/viewtopic.php?f=4&t=373&p=3788

From the answers that mgrigs got from the company representative there - "Likely to have a 10 year battery warranty"

I readily admit that this rumor could be based on the whole California requirement which doesn't apply since the Leaf isn't a hybrid. We will have to wait and see.

Some e-vehicles do not do individual cell management.

But, using most of the LEAF's cell's capacity (perhaps 90% down to 10%), it is likely that the LEAF will do cell monitoring and some form of cell balancing.

My e-motorcycle has twenty one 60 amp-hour cells, and I can monitor all the cells, collect and graph data, and balance the cells while finishing charging.

I know, comparing the Toyota RAV4-EV to the Nissan Leaf is not really popular - but...

Toyota would replace batteries (while they had them) when the owner could show 80% degradation during the warranty period.

What would have satisfied almost every RAV owner would have been the availability of replacement batteries. Once Toyota/Panasonic lost the patent infringement suit brought by Texaco/Chevron then no batteries were available, at any price. Even though it is known which modules go bad first, and how to replace them - there are no batteries to replace them with.

As long as Nissan can provide batteries (modules) as needed, I'm not worried about "bad modules". They are replaceable.

Dav said:

As long as Nissan can provide batteries (modules) as needed, I'm not worried about "bad modules". They are replaceable.

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Absolutely! And better yet - Nissan's AESC isn't the only company making LiMn cells so in the unlikely event of a water land...I mean in the unlikely event that AESC closes their doors, we'll be able to hack the pack until another vendor makes cells in the same physical size/capacity.