By George S. Bower

Note - GSB told me he had an article for you today. Normally we'd run a Volt sales story, but we can break tradition and cancel that. Just kidding! (kdawg, those last two words mean j/k ... j/k.). :). Not that everyone doesn't already know it, but Volt sold 1,788 units in July to Leaf's 1,864 . Calendar YTD, Leaf is up by 60 units at 11,703 sold. Comparing July 2013 to July 2012 , Leaf's doing really well and is up 371.9 percent over the mere 395 units it sold in July 2012 versus Volt's 1,849 sold in July 2012. YTD compared to 2012, the Leaf's tally is up 270.3 percent. Calendar YTD in 2012, Volt was at 10,666 units. This year Volt's at 11,643 CYTD. In short: Volt is mildly ahead, and Leaf appears to be coming on stronger, but also, Nissan practically had no where to go but up.



We saw in another article presented here that the Spark EV co axial transmission offered some advantages relative to simplicity, weight and packaging compared to the Volt transmission. Could the Spark's battery offer some advantages over the Volt battery as well?

We all know that the Volt uses a “T” pack configuration as shown in figure 1.


The Spark battery has 336 prismatic shaped cells like the Volt only configured in a square box that fits under the rear seat and in and below the rear hatch storage area as shown in figures 2, 3 and 4.


Battery Stats


A comparison of the Spark and Volt battery is presented in figure 5


The Spark's battery is rated at 21.4 kwh versus 16.5 for the Volt…….not surprising since the Spark is a pure EV designed to go 82 miles on a charge while the Volt is an extended range vehicle designed for 40 mile EV range.

Also not surprising is that the Spark battery pack is larger volumetrically at 133 liters versus 100 liters for the Volt and also heavier at 560 lb versus 435 lb for the Volt.

The Spark pack uses a much higher percentage of its rated capacity at 81 percent versus 65 percent for the Volt. This may be due to the robust nature of the packs Fe chemistry relative to number of charge cycles, tolerance to heat and tolerance to high charge rates. This tolerance to high charge rates shows up in the Spark's ability to charge to 80 percent of full charge in 20 minutes while the Volt has no quick charge capability. Translated into C rate, we see the Spark's battery can charge at 2.3 C…..pretty high by any automotive standard.

I mentioned ruggedness and tolerance to high charge rates and high temperatures as a virtue of Spark's Fe chemistry.

Little known is that the Spark uses a much simpler cooling scheme than the Volt. As shown in figure 6, the Volt uses aluminum, liquid cooled plates between every other cell. The Spark however uses only 2 thermal exchange plates (separated by a thermal matt) located in the bottom of the battery box resulting in a simplified, lower cost and higher reliability design as shown in figure 7.


When looking at the Spark battery, one is tempted to say that the pack looks smaller than the Volt. We know it is larger than the Volt at 133 liters versus 100 for the Volt but it also has a much higher kwh rating so while the pack may be 33 percent larger in Volume it also has 60 percent more energy. So on a volume per kwh basis the Spark pack is actually smaller than the Volt. These figures are shown in figure 8.


Which battery is better? There are trade off of course but personally I think the Sparks battery is better. It is more robust, can handle higher charge rates and has a simpler, lower cost cooling scheme.

I think this battery would make an excellent choice for Volt gen 2.0

What do you think?

Hat tip to WOT who mentioned the battery cooling in the tray via the GM-Volt forum.