Battery longevity factors?

jray3 wrote, in part --
"Here's a very good study on the LEAF battery. http://www.mynissanleaf.com/wiki/index.php?title=Battery_Capacity_Loss "

That's a fascinating and informative page on what extends and depletes life of these kinds of batteries. Thanks!

On of the dominant factors shown there is temperature.
Higher is worse. Per their graph in best of all worlds the battery should sit at about 45-degrees farenheit..... All other things being equal much lower life span at 90-degrees.

That raises two questions at least:
Does that (low temp good, high temp bad) apply equally to a battery sitting inactive in the garage as to one actively charging and discharging?
Does the MiEV battery cooling system actively cool it while it's sitting on the charger in the garage? I ask because our garage can get up to 90+ in the summer.

The other thing in that article is that the average state of charge the battery is kept in effects the longevity an almost counter-intuitive direction.
The lower state of charge it is in the longer it lasts.
(of course this is only counterintuitive from a history of conventional lead acid batteries.)
If I'm understanding that right, the take-home message would be to NOT fully charge your MiEV if you don't expect to need to run the full 60 miles on it in the forseeable future.
That is, if your normal pattern of use is, say, 12 miles out and 12 miles back home, that you'd be better taking it off the charger after it's, oh, say, 70% charged than leaving it on to 100%.

That make any sense?

Alex

I believe all of your assumptions are correct, for whatever that's worth. We try to use the car pretty much as you describe

The battery management system never fully charges the battery, so Mitsu has taken a giant first step in adding life to the pack - It also won't allow you to 100% discharge it either. From everything I've read about lithium technology, not charging it until it's mostly discharged and then not 'fully' charging it are both good for it also. Since we usually only use the car for 10 to 30 miles a day, we mostly try to plug it in for a few hours now and then to add a few bars to the pack without fully charging it . . . . except for the rare occasion where we think we'll need to go 50 or 60 miles. It gets fully charged once a week or so, but it gets lots of partial charges which only add a few bars several times a week also

It *will be* interesting to see how long the battery lasts vs how other drivers are using their car - There are owners who regularly drive 80 or 100 miles a day, recharging fully twice each day . . . . and then there are those who drive 10 or 15 miles per day, recharging every 4 or 5 days. It will be interesting to see if either of those scenarios has a marked effect on the ultimate battery life

As to temps - I don't think 90 degrees is hot enough to have a big effect on battery life - The Leafs that were experiencing problems were mostly all being used in much hotter climates than that and then I think everyone believes that the Mitsu active cooling system is much more efficient than the Leafs passive system

Time will tell all

Don

Don said:

... As to temps - I don't think 90 degrees is hot enough to have a big effect on battery life - The Leafs that were experiencing problems were mostly all being used in much hotter climates than that and then I think everyone believes that the Mitsu active cooling system is much more efficient than the Leafs passive system...

Click to expand...

Thanks Don, for your typically informative response.

Still curious, if anyone knows about my other question:
When the car's sitting on the charger in the hot garage (so let's say for sake of discussion it's Pheonix Arizona in August and 125 degrees in the garage) does the Mitsu active cooling system for the battery kick in?

Alex

Yes, it does

From a Mitsu advertising brochure:

"TWO LITHIUM-ION COOLING SYSTEMS
Our custom-made main drive lithium-ion battery pack is equipped with a fan-driven, forced-air induction system that automatically engages to protect the battery from overheating during charging. With the public quick-charger option, you'll be happy to know we've also added an air-cooling system that draws cold air from the air conditioning unit to counter the excessive heat often produced by quick-chargers. Either way, your batteries are kept nice and cool, even in hot climates."

Don

Hi Guys,

I can't help but think that all of this just makes normal common sense.

I look at it as the battery only has a certain amount of total energy it can accept and then deliver back. So it makes sense that you get more cycles if they are smaller cycles. I don't think that people that are doing higher mileage should worry they will probably use up the pack faster but those of use that are doing less mileage will suffer from the battery deteriorating from the shelf life effect. The only thing that is really clear is heat is bad and full charges are bad. Also driving inefficiently is also bad (as it is with ice cars).

From reading the leaf web site above it looks like the battery will last 5 years at least even if it's tortured. Even then your still at 70 % the car is still usable, hopefully that 30% hit still allows you to get to work and back.

For those of us that baby the car baring cell failure I think the battery will outlast the car (at least in my climate where road salt causes rust that kills car in 10-15 years). So personally I'm not too worried but I think as with all members of the family it's best to keep them in the house (garage) as much as possible. Your already heating and cooling the house so just pass that along to the car and it will last a long time. If you live in a really hot area then do what you can to keep the car cool and drive it gently/park in the shade.

Don.....

Don said:

Our custom-made main drive lithium-ion battery pack is equipped with a fan-driven, forced-air induction system that automatically engages to protect the battery from overheating during charging.[/b]

Click to expand...

So for those with really hot garages, charging would only circulate hot air from the garage which might not be sufficient to reduce the battery pack's temperature. However, Level 1 and even Level 2 charging amperages are much lower than those involved with propelling and regeneratively braking the car, so I wonder how much heat is generated during Levels 1 or 2 charging. It might be so little that overheating during Levels 1 or 2 charging isn't a serious concern. Of course, this doesn't apply to fast Level 3 DC charging, but that's not going to occur in a hot garage, and the car's A/C system would activate to keep the battery pack cool, so Level 3 charging shouldn't be a concern, either.

In my experiences last summer, I've never heard the battery cooling fan come on. Ambient outside temps here on the Gulf are sometimes as high as 95 (frequently with 80% humidity) but my garage is always at least 10 degrees cooler than the outside temps (it's frequently 10 or more degrees warmer in the winter too . . . . I regularly look at the temp display in the car) and to the best of my knowledge, the battery has never needed cooling . . . . *if* I don't recharge immediately after use. If I've driven any distance at all, I always wait an hour or two before charging, because as you say, the discharge currents are much higher than the charge current, so it make sense that the battery is at it's warmest right after powering the car

If I lived in Phoenix, temps could probably come into play and maybe reduce the battery life somewhat, but then I think temps in the range of what they see every summer in Phoenix will shorten the life of just about everything we use, not just our cars. I just don't see temps below 100 or so as having much adverse effect, especially if you regularly garage your car . . . . but like everything else, we'll know lots more after a few years of use

Don

Here in Dallas, it gets quite hot in the summer. Temps around 100°F are not unheard of. Last year, I added a powered attic exhaust fan, and started opening the hatch to the attic from the garage with the thoughts that it would keep the garage cooler. (This was before I got the i-MiEV.) It seemed to work, so that's something to consider if you live in a hot climate.