GaslessInSeattle said:
Bill, you have a persuasive argument. I have not heard the first responder guide referenced before and that is a place where anything less than full disclosure could be deadly and full of civil liability. The fact that the 403.2 volts number meets up exactly with your calculation is rather sobering, but my knowledge of electricity is very limited.
Assuming what you are saying is true and assuming I'm getting it right, those of us who routinely charge to 100% could expect to see the battery degrade 1.6 times faster than if we went to 80% charging. I would think Nissan must be basing their 100,000 mile warranty on the assumption that using up the battery at the 1.6 rate would land the battery at a little above 80% capacity over 8 years/100K miles. Since industry standard is to consider the battery dead once it's below 80%, it would seem wise for Nissan to use that standard as their benchmark for warranty or risk seriously upsetting the popularity of EV's. Another way of putting it is, perhaps Nissan is saying that if you want to significantly increase the longevity of the battery beyond the warranty period, then charge to 80% mostly. If what they are saying is that if we charge to 100% on a regular basis and the battery reaches 80% capacity or worse prematurely, that it's on us, then we have a problem.
The following is a lift from the LEAF site FAQ. It looks like Nissan is saying they base their life projection on 70%, which extends cycle life considerably, especially at 80% charge. Also, note that the data referenced in my last post is based on full discharge (?) to full charge cycles, and multiple shallow discharges add up to a full discharge.
Q: How many charging cycles can the energy storage device survive?
A: Like all lithium ion batteries, the Nissan LEAF battery will experience gradual capacity loss over time. We expect the battery to last over 10 years, however, there may be a gradual loss of capacity of 30% or more depending on your driving patterns, and the effect on your battery. The battery can be used afterward for storage applications. (My note: Wonder what that means, “used for storage applications”)
The other curve I'm trying to understand is where this 1.6 factors into the expected degradation of the battery due to time, not just in terms of number of cycles. Is time or cycles going to be the limiting factor here. Also, depending on how sophisticated the charger of the Leaf is, charging a large bank of batteries, allowing for different rates of charge to different sectors and so on, may result in a different decay curve than what we are reading about in the article linked.
As best as I can determine, time alone is not big factor in determining cell life. But, Li-Ion should not be stored at full charge for extended periods, and storage at high temperatures is also detrimental. For example, laptop computers are often used as a primary computer and left connected to the AC for extended periods – even 24/7. Under those conditions, it is recommended that the Li-Ion battery be removed.
I know no details of the charger, but I would bet money it has provisions for insuring the cells remain in balance. It would be technically quite easy to monitor each module’s voltage and adjust the charge to that module. Another laptop analogy. Unbalance is a reason why they seem to fail rather early. Cell voltage is monitored but not adjusted, so if a cell approaches a dangerous voltage, the entire charge is shut down, resulting in some cells not receiving a full charge. The danger of fire is almost eliminated, but the unbalance gets progressively worse, and soon the battery duration drops to zilch. That should not be the case with a well designed charging system.
Another curve I'm trying to get a handle on is how quickly these batteries will become outmoded technologically, as economy of scale and battery technology bring the price point down for a dramatically extended battery pack, likely within a few years rather than the better part of a decade (the warranty period), it may not matter if we all work the piss out of these batteries because chances are that we are going to be upgrading them sooner than they wear out anyway, when the 200 or 300 mile battery is available and at a price that makes it tempting enough.
Those bettery batteries are out there - just not ready for high current use or competatively priced.
If charging to 100% kills the battery within say 4 or 5 years then charging to 80% will probably be compelling to me. The problem is, if we really are allowed to access 100% of the batteries discharge/charge capacity, and seeing that the actual expected range with highway driving is more like 73 miles, and you add in a reasonable reserve like say 10 miles, you really only have a 60 mile range. This may still not turn out to be a big deal if true since that is more than the average person drives in a day, accept that it cuts down on spontaneity, particularly for those of us relying on the L1 charger. I think L2 is going to be my friend once I get it installed. I'll be curious to see of I can be part of the 80% club and still meet the flexibility needed for our spontaneous lifestyle once charging with L2 primarily. Good news is that it looks like we've gotten the green light for the free installation!
Congrats on the free installation. I rent and do not care to go through the hassle of getting landlord permission (if even possible), permitting, and inspection, so L1 will be my charge of choice. I am retired and rarely take a car out of the garage more often than every other day. Groceries, Doctor, recreation, and food and drink are within the 80% range, I think.
Bill