One Year of Battery Capacity Data

67goat · May 4, 2017

I go to Grass Valley for a bluegrass festival each year. It is a nice area. The first time I went in my Spark I was really worried, between the distance and the slope, I wasn't sure I could make it. Luckily, the sheriff's office has a L2 charger they let me use.

d15b7 · May 4, 2017

i've been keeping an even closer eye on this the last 6 weeks now. i'm convinced that ambient temp has a significant impact on the actual battery capacity of our Spark EVs (mine is a 2015 with 20k miles). the last week or two it has been very nice weather here (70s-80s during the day, high 50s low 60s at night). I have been driving the same commute and using the car the way I always do. my observations have been that my calculated battery capacity is now pretty steady at 17.9 to 18.0 kwh (in the colder months the capacity calculates out to 17.1 to 17.4 kwh. nothing has changed other than the ambient outside temp. this leads me to believe that the battery itself isn't as efficient at storing energy when it is 30-40 degs outside as it is when it's over 60 degs outside.

Zoomit · May 4, 2017

My data on the original post showed no discernible correlation between seasons and battery capacity estimates. My seasonal temperature variation is about 50 degF.

d15b7 · May 4, 2017

Zoomit said:
My data on the original post showed no discernible correlation between seasons and battery capacity estimates. My seasonal temperature variation is about 50 degF.

hmmmm that's puzzling; mine most definitely does vary with temps. maybe it's the temp range? my low temps here in the winter are teens/20s. the battery capacity definitely (on mine) is lower when it's around ambient 40 (or lower). capacity noticably goes up when ambient is 60s or above.

does yours live inside or outside? I don't have a garage (at least not for my Spark; my 3 garage spaces are occupied by two race cars with no glass and my stock C4 ZR-1. Spark is relegated along with pickup truck to outside at all times!). so overnight the Spark gets cold and stays that way.

the battery management system rarely steps in during the summer (it doesn't get warm enough here i guess). in two years i've only seen the battery conditioning turn on one time during the summer. during the winter when it's below 25 deg I often see the battery conditioning showing a percentage of use. (that's neither here nor there when it comes to total capacity, but just thought i'd share what the Leaf screen says is going on related to temp out here).

as an aside, I'm a race driver and I race a special EV Sports Racer for Entropy Racing (it's called an EVSR). now that car is very sensitive to cold batteries (anything below 50 ambient). we get false/erroneous 'low battery-low voltage' warning from it if we don't warm the batteries by running the car gently for 10 minutes before a qualifying session (or we can charge it a couple hours beforehand and time it to disconnect right before going out on track). once the battery packs are warm (we have 25 cells on each side of the car in low pods) they stay warm enough for the rest of the day. but that's apples to doughnuts compare to our Sparks; we use a 25 kwh total battery capacity and they are lithium ferrous phosphate chemistry. (why you ask? because we need something very stable in a road race car; accidents/crashes are common and I didn't want to be in between two exploding battery packs!). so those packs aren't as energy dense as our Sparks are, but they can't catch fire or explode and they can be overheated or over-amped with little danger.

Zoomit · May 7, 2017

I too would have expected to see a seasonal variation in capacity. Physics says it's there, and so it may be masked by my particular usage. I definitely see a seasonal variation in driving efficiency for my morning commute. I leave the car outside and it might be 30-40% less efficient in the morning. I haven't seen a seasonal variation in my return commute. The fact that I drive downhill in the morning and uphill in the evening may affect the results. I'm not sure.

d15b7 · May 7, 2017

Zoomit said:
I too would have expected to see a seasonal variation in capacity. Physics says it's there, and so it may be masked by my particular usage. I definitely see a seasonal variation in driving efficiency for my morning commute. I leave the car outside and it might be 30-40% less efficient in the morning. I haven't seen a seasonal variation in my return commute. The fact that I drive downhill in the morning and uphill in the evening may affect the results. I'm not sure.

I definitely see your same lower efficiency due to low temps; if it's 35 deg outside when I leave for work, I'll struggle to see 4.4 mi/kw on the gauge (that's with zero heat turned on, no seat heaters, etc). the capacity readings on those days will be in the 17.2 kwh range. when it's 80 deg outside, the same exact drive will be 5.5+ mi/kw and the battery capacity calc will be roughly 17.9 kwh.