Bolt battery capacity speculation -> 65kWh

From this image on the Chevy Bolt EV website:


...we can infer the useable battery capacity is about 65 kWh. This is based on using 18.1 kWh for 28% of the battery (18.1/0.28 = 64.6).

I do this calculation all the time to measure the battery capacity in my Spark EV, to create trend data for capacity loss.

HOWEVER, that's a huge battery! You could also infer from the same data that the predicted total range for that charge is 281 miles (78.7/0.28 = 281). Frankly, a 65 kWh battery yielding 250+miles range doesn't seem legitimate for the Bolt. That would put it right at the Tesla Model S 70 level. We shall see...

I should mention that this calculation only works if you don't partially recharge the car since the driving away from the "last full charge". GM probably did just that, partially recharged the battery, before they took this image. Doing so would mask the actual battery capacity. So maybe the most accurate interpretation of this image is that the useable battery capacity is NO MORE than 65 kWh.

According to Motor Trend, the battery charges in 9 hours at 240 V 32 A, approximately 69 kWh. If we assume 80% charging efficiency, this gives about 55 kWh usable.

55 kWh/200 miles would be about 275 Wh/mile, a reasonable figure.

While there are real-life variabilities in those numbers, GM did specifically state 9 hr, 240V, and 32A. However I think Level 2 charging efficiencies are closer to 90%, especially at 7.5kW.
http://ieeexplore.ieee.org/xpl/logi...7038626/7046205/07046253.pdf?arnumber=7046253

That implies a 62 kWh battery, which could mean range beyond 250 miles under favorable driving conditions (little climate control, flat land, no speeding, etc).

That's about what I figure too:

18.7kwh used for 78.7miles.
18,700wh/78.7m => 230wh/mile
230wh/m * 200miles => 46kwh usable.

With a margin for error, we are looking at a 55kwh – 60kwh battery pack.

The 2nd gen Chevy Volt EPA gets 3.7 miles/kWh. Compare to the Bolt EV which looks taller and just as wide as the Volt, but the powertrain and aerodynamics could be slightly better, so we can assume similar efficiency to the Volt overall.

200 mile range at 3.7 miles per kWh would make a usable battery pack of 54 kWh, and with 80%-85% usable, the overall size would be 65kWh to 70kWh.

That's a Tesla sized battery.. in a compact car!

If it starts at $37,500 I think even late adopters will find the Bolt appealing.

Zoomit said:

While there are real-life variabilities in those numbers, GM did specifically state 9 hr, 240V, and 32A. However I think Level 2 charging efficiencies are closer to 90%, especially at 7.5kW.
http://ieeexplore.ieee.org/xpl/logi...7038626/7046205/07046253.pdf?arnumber=7046253

That implies a 62 kWh battery, which could mean range beyond 250 miles under favorable driving conditions (little climate control, flat land, no speeding, etc).

Click to expand...

I was giving some allocation to slowing of the charging near completion and used 80% as a guesstimate to wrap everything together.

Ford Focus Electric: 240 V 30 A 3.5 hours in = 25.2 kWh in, 19.5 usable, 77%. But as you say, actual electrical efficiency is higher, this is just a basis of estimate. Taper of charging is unknown.

Also....hopefully Bolt uses aggressive battery thermal management as does Volt. In this case, overall charging efficiency will appear lower due to energy consumed by cooling system

Looks like it'll be 60 kWh with "liquid active thermal control"

http://insideevs.com/chevrolet-bolt-ev-specs-revealed-60-kwh-0-60-in-less-than-7-seconds/

http://insideevs.com/chevy-bolt-200-mile-ev-battery-cooling-and-gearbox-details-bower/

I found this article had good info on the cooling and gearbox