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Before the Chevy Volt (a plug-in hybrid) went on sale,听Volt Chief Engineer Andrew Farah听openly acknowledged that the extreme temperatures found in the Southwest have the potential to permanently reduce the battery pack鈥檚 capacity to store energy:

So what is a manufacturer to do if a given customer鈥檚 driving habits consistently exposes his or her battery pack to excessively high temperatures in a place like Tucson, or charges it five times a day, or maybe applies a blowtorch to it? As it turns out, the answer depends on what the warranty says, not so much on what the owner鈥檚 manual warns you not to do.

As the chief engineer for the Volt warned above, Nissan鈥檚 owner鈥檚 manual also warned that excessive exposure to ambient temperatures above 120 degrees F would degrade battery capacity. However, when a handful of Leaf owners in the Southwest realized that their batteries were losing capacity faster than batteries not repeatedly exposed to temperatures over 120 degrees F, they filed a class action lawsuit.听

How听Nissan responded:

听How does the new Leaf warranty compare to the Volt warranty?

Nissan claimed that they were听鈥�..the first and only manufacturer in the automotive industry to provide limited warranty coverage for battery capacity loss for electric vehicles.鈥澨�It鈥檚 possible the Volt was left off that list because it鈥檚 a plug-in hybrid as opposed to being a fully electric vehicle, or they left it off because it isn鈥檛 clear what the Volt battery warranty covers. At first glance, the听Volt warranty听also appears to guarantee 70 percent of battery capacity at the end of the warranty period except it makes that claim in the section of the warranty for听component defects related to materials or workmanship:

The list of components following the statement 鈥�component defect related to materials or workmanship鈥�includes: High Voltage Wiring, Voltec Control Modules, E-Compressor, Traction Power Inverter Module, Accessory Power Module, On-Board Charger 鈥�and, uh oh, the Propulsion Battery.

But all electric cars come with a warranty that covers component defects related to materials or workmanship. What those manufacturers didn鈥檛 cover (until Nissan鈥檚 announcement) is battery capacity loss if, as the Volt chief engineer said,听鈥� 鈥�you live in the Southwest, depending on how you use your car鈥� 鈥�

By placing the propulsion battery in that list of components covered for defects related to materials and workmanship, GM has muddled the answer to the question of whether or not a Volt battery degraded because听鈥� 鈥�you live in the Southwest, depending on how you use your car鈥� 鈥澨�听is really covered for things like hot parking lots. Lawyers, where would we be without them?

The Volt warranty went into great detail about how they would fix or replace a battery 鈥�that is listed along with all of the other Voltec items covered for a defect related to materials or workmanship:

The Volt and听 Electric Ford Focus听 have an active battery thermal management system that cools the batteries in the same way that most car engines stay cool; by pumping antifreeze over the hot batteries to a radiator that is in turn cooled by a fan, however, the coolant pump and fan work only when the car is running. Not that it would do any good to leave the Volt running in a Tucson parking lot with a 140 degree surface temperature as some听Volt enthusiasts discovered听when investigating this issue:

As if that were not an expected result. As mentioned by the Volt chief engineer, all lithium battery powered cars share this vulnerability to things like very hot parking lots.

From the听Ford Focus Owner鈥檚 Manual:

Bottom line, if your electric Ford Focus (or Volt for that matter) sits too long too often in hot Southwest parking lots, or if one of the dozens of the coolant system鈥檚 rubber hoses, or connectors, valves, or water pump fails or even if you have the wrong mix of water and coolant in your radiator your battery could get toasted and not be covered by the warranty.

听From the听Ford Focus Warranty:

听From the听Tesla Warranty:

听Why was the Nissan Leaf the first to test the warranty waters?

1. Somebody had to be the first.

2. There are more Leafs out there than any other electric car (the Volt is a plug-in hybrid).

3. The Leaf has a rather obvious indicator gauge that actually warns the owner that the battery can鈥檛 hold as much charge as it did when brand new (12 indication bars is full capacity, 9 bars is 75 percent). My Leaf is approaching 20,000 miles and the battery capacity gauge still shows all 12 bars. Why Nissan thought it was important to provide that information, I have no idea but it probably contributed to their being the first to deal with battery degradation not caused by workmanship or defects. To get that information on an electric Ford Focus requires a 24 hour test at the dealership.

4. Some concerned Leaf owners found that there was nothing wrong with their battery after all. The gauge was simply miscalibrated.

5. Another factor may have been that the Leaf owner鈥檚 manual actually quotes a not to exceed value of 120 degrees while most other manufacturers are more vague, never actually quoting a number. After reading their manuals, many owners in the Southwest were concerned by the fact that their car may have been exposed to temperatures higher than that.

6. Range degradation would be much less noticeable with a plug-in hybrid where the engine simply takes over as is the case with the Volt.

听Active liquid-cooled thermal management verses passive air-cooled thermal management

Electric听Ford Focus cooling system

The word 鈥渁ctive鈥� implies that the system uses moving parts like pumps, flowing liquids, fans, and valves. 鈥淧assive,鈥� of course, implies no moving parts. Ultimately, both systems are air cooled but in the active system the heat has to be moved via a hot liquid to a radiator before the air can cool it, so the title could be shortened to 鈥淎ctive thermal management verses passive thermal management.鈥�

The Leaf鈥檚 competitors have jumped on the bandwagon to make hay while its cooling system weathers the onslaught of various bloggers, conspiracy theorists,听 and wiki authors by portraying that Rube Goldberg collection of parts in the video above that is their cooling system as if it is a good thing. If complexity is a good thing, the Volt, with its five radiators, wins, hands down.

A good place to start seeking evidence that the Leaf鈥檚 method of controlling battery temperatures听 is inferior to a liquid thermal cooling system would be via battery warranties. But, as discussed above, until recently with the Nissan warranty, none of the manufacturers鈥� warranties cover owners for thermal damage quite simply because they can鈥檛 control everything consumers are wont to do, like leave a car in a Tucson parking lot.

Will the Leaf become the Prius of electric cars?

When the Prius first arrived its competitors claimed it was a money losing, unreliable, engineering farce that actually consumed more lifetime energy than a Hummer. We all know how that story ended.

At this point you may be wondering 鈥︹�滺ow does the Leaf keep its batteries from getting too hot without resorting to the pumps, coolant, radiators, hoses, valves, and fans (see听 above photo)? As with the Prius and its unprecedented mileage, their solution is pure elegance. Instead of cooling batteries down, they don鈥檛 let them get hot. According to an interview in the听Nissan Technology Magazine听with Takeshi Miyamoto, (taking a deep breath 鈥�Engineering Director of EV Technology Development Division, EV Energy Development Department, Battery Engineering Group) the temperature is controlled by adjustment of the battery鈥檚 internal resistance. Of course, you can鈥檛 physically go inside a battery and alter its internal resistance but the internal resistance expressed is different depending on whether it is being discharged, or charged, and how fast that is happening, and at what temperature.

Translation: The computer controls battery internal resistance by varying performance parameters while letting battery temperature float up or down in a safe range. For example, I鈥檝e noticed that my Leaf does not allow much, if any regenerative braking right after a fresh recharge. Regenerative braking does not return in full force until the batteries cool and/or discharge to a lower level. From the听Leaf owners manual:

Suppose you鈥檙e driving 80 mph up a mountain on a 120 degree day and the battery temperatures approach a level that could cause damage. The car鈥檚 software slows the car down (reduces power draw from the battery pack) as much as needed to keep the temperatures in a healthy range (and the car at a safe speed). If you are in stop and go traffic on a 120 degree day, if necessary, it will limit how fast your car can accelerate, and how much it can regenerate, etc, etc, to the point of shutting the car down in steps to prevent battery damage if necessary or if acceleration or top speed is too limited for further safe driving.

The car wouldn鈥檛 suddenly shut down. As with a low battery charge condition, it would begin by giving you warnings to get the car to a safe parking spot before finally going into Turtle mode, which will only allow the car to move maybe five miles per hour long enough to get to a safe spot. How often does a Leaf have to go into Turtle mode to protect the batteries? It must be a very rare event because I have yet to find with Google searches anyone who went into turtle mode because of high battery temperatures. On the other hand, as mentioned earlier, my Leaf鈥檚 computer often limits the car鈥檚 ability to use regenerative braking, in which range is traded off for speed and acceleration.

After reading parts of the Ford Focus owner鈥檚 manual, its obvious that they also have a limited ability to vary performance to control temperature. It has a warning indicator message that reads听鈥淪everely Limited Performance Due to hot battery鈥澨�which means听鈥� vehicle performance is severely affected by hot battery temperatures. Drive with caution. Keep vehicle plugged in when not in use to maintain proper battery temperature.鈥澨�But that sounds more like an emergency measure as opposed to a design feature.

Simply put, the Nissan engineers have fine tuned their software, battery limits, and car performance in such a way as to not need a heavy, complex and expensive, active liquid cooling system. Leaf drivers rarely notice the performance changes happening to keep the battery pack cool. I鈥檝e never noticed my battery temperature gauge moving at all.听 It is in some ways analogous to the fine tuned design of the Prius which remains unmatched for gas mileage performance after all these years. The consistent high ambient temps in the Southwest punched through the Leaf鈥檚 design envelope for a small number of drivers. They鈥檒l get it under control, possibly with this new battery:

From听Green Car Reports:

I suspect that the Leaf may very well prove to be the Prius of the electric cars. The Leaf solution to controlling battery temperatures is actually technologically superior in just about every way to the primitive, ham-fisted system of hoses, pumps, fans, valves and radiators used in cars since the Model T 鈥� and in WW II era fighter planes I might add.

Every aircraft I have ever flown, or have ever been a passenger in, uses passive (requiring no moving components) air cooling for the engines (no fans, pumps, liquid coolant, hoses, or radiators), except one, a WW II era P-51 mustang fighter I once hitched a ride in. I had an old professor who had helped to design the system of shut off valves for that plane to prevent loss of coolant from bullet holes. Unlike the air cooled fighters and bombers, a single hole in the cooling system could bring a Mustang down.

So, obviously, if听 aircraft use passive air cooling, it must not only be adequate for cooling, it must also have some advantages over active liquid cooling systems in some applications. For commercial aircraft the two overarching reasons are:

1. Less weight which translates into greater efficiency (the compact four passenger听Volt weighs听over 400 pounds more than a mid-sized听five passenger Leaf, although not entirely due to its cooling system).

2. Greater reliability via less complexity (fewer components like hoses, connectors, pumps, valves, and radiators to fail). The Volt has five radiators.

For the Leaf, you can add to that list, less cost.

In my life I have experienced dozens of instances in my cars or in the cars of people I know, of failures in the coolant system. One failure like that with a battery that relies on a pumped coolant is likely to permanently damage it, or at least to cause the computers to shut it down.

Source:听Testing听the Electric Car Battery Warranty Waters