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EV Articles by Paul Gipe

December 23, 2021
Paul Gipe

Battery Degradation 2020 Bolt Relative to 2017 Bolt EV

With our Pandemic Peregrinations we’ve driven our 2020 Bolt EV far more during its first year of operation than we did our previous 2017 Bolt during its first year. We drove the 2020 Bolt about 50% more during its first year (~15,000 miles) than we did the first year of our 2017 Bolt (~10,000 miles). You’d think that we’d see more traction battery degradation as a result, but that’s not the case. In fact, we see less--about half less.

First, the caveats. This is anecdotal, I am only looking at two cars, not a fleet. I am only going to use the “percent” method of calculating the traction battery capacity.

Previously, I reported on the degradation we saw in our 2017 Bolt after our three-year lease expired (see Slight Chevy Bolt Traction Battery Degradation after Nearly 30,000 Miles). In that report I used three methods to gauge degradation: the percent method, range estimates, and the OBD scanner reports on capacity.

Varying range estimates over time are not a reliable way to gauge degradation.

GM changed the signal from the car’s computer for traction battery capacity in the 2020 model Bolt relative to previous models so I didn’t collect any OBD scanner data on capacity. Later in the year Bolt data guru Sean Graham and other data nerds determined the OBD2 “PIDs” for the 2020’s battery capacity. So now I am collecting the data, but I missed much of the first year.

Nor am I going to produce time-consuming charts. Instead, I’ll simply post the results of the linear regression analysis of the data for the two models.

Disclosure: I worked for GM's Delco-Remy Division 1968-1970 as a cooperative engineering student. I was a member of UAW Local 1981 until the National Writers Union left the UAW in May 2020. The Chevy Bolt is assembled by UAW Local 5960.

To compare apples to apples, I chose to compare the same mileage between the two models as opposed to the calendar period. I compared degradation for ~15,000 miles of travel.

The linear regression analysis found that the y-intercept for the 2017 Bolt was 61.7 kWh and that for the 2020 Bolt was 64.4 kWh. This is effectively the capacity that both cars started with. The x-coefficient was 0.0002 for the 2017 Bolt and 0.0001 for the 2020 Bolt.   

Early indications are that the rate our 2020 Bolt is degrading is about one-half that of the 2017 Bolt.

The question of degradation is now moot. GM is replacing the batteries in both model years because of the battery-fire recall. We expect a brand new battery courtesy of GM sometime in 2022.

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