One of the first electric cars to make it onto American roads, GM’s Chevy Bolt has gained a strong following of environmentally aware motorists. However, as is often the case with early adopters, GM’s LG Chem-sourced battery packs have at times been problematic, resulting in vehicle recalls to update software and even replace the complete pack under warranty.

With over 100,000 Bolts on US roads, it’s no surprise that owners are asking questions about battery life, and in particular, how much the Bolt’s battery should deteriorate over time. For most owners, this deterioration will be seen as a reduction in driving range, as the battery ages.

The Bolt debuted with a 239-mile range for both the LT and Premier trims. Starting with the 2020 model year, GM increased the Bolt’s range to 259 miles per charge for both models. Unlike vehicles such as the Tesla, where variants are differentiated by powertrain, the main difference between the LT and Premiere Bolts are infotainment and safety upgrade packages.

So, as the battery degrades and the range decreases, many Bolt drivers are uncertain about what the normal rate of degradation ought to be, and when the battery should be replaced?

This Is How Much A Chevy Bolt's Battery Should Deteriorate Over Time

Instrument Display Cannot Show If The Chevy Bolt's Battery Deteriorates Over Time
Via: InsideEVs

Normal battery degradation is determined by two things: The age of the battery - also known as 'calendar' aging - and how the battery is used and charged.

Based on the data gathered by Recurrent, a Seattle startup that provides independent reports on the condition of EV batteries, it would appear that, although the battery is liquid-cooled, the Bolt functions best at ambient operating temperatures of between 60 and 90 degrees Fahrenheit. With a daytime temperature of about 30 degrees, the driving range drops by 60%.

However, whilst cold daily ambient operating temperatures have a significant impact on the driving range, short periods of cold-weather operation should not play a significant part in the rate at which the battery degrades.

Continued exposure to high temperatures coupled to fast charging from very low levels of SoC (State of Charge) however, can significantly increase the rate of deterioration and shorten battery life.

According to GM’s electric car warranty, a Bolt’s battery would be considered for replacement when its capacity drops below 60% of that of a new 60 kWh battery. This means that GM will cover the replacement costs of the battery should the capacity drop below 36 kWh. Obviously, this will manifest as a similar reduction in driving range.

In other words, when a fully charged Bolt that is rated to travel 238 miles on a full battery only covers 143 miles, GM would consider this a valid warranty claim. Of course, this only applies to vehicles within the warranty period.

According to information sent to GreenCarReports by Fred Ligouri of Chevrolet Communications, a battery pack replacement not covered by warranty would cost around $16,000, so it’s important that you understand the terms and conditions of the electric car battery warranty.

However, with Bolt batteries typically degrading at about 6 to 8% over 100,000 miles, battery replacements are not an everyday occurrence.

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This Is How To Measure A Chevy Bolt's Battery Deterioration Rate

Using The Bolt's Battery Percentage Display To Determine The Chevy Bolt's Battery Deterioration
Via: Green Car Reports

After a battery management system (BMS) update, Eric Way of “Torque News” was unsure of the condition of his Bolt’s battery and so decided to calculate the actual degradation as his vehicle approached 100,000 miles.

Before the update, at 70,000 miles, Way had calculated that his Bolt EV had lost about 8% of its original capacity. However, after the trip to the dealer, he encountered a discrepancy in his data, suspecting that the 8% battery degradation he measured at 70,000 miles was, in fact, an inflated figure.

Thus, with the vehicle approaching 100,000 miles he set out to once again measure the degradation.

Starting with a fully charged battery Way covered 200 miles before stopping for the first charge. At this point, he recorded the energy used and the battery percentage displayed on the readout. Using this information the estimated capacity remaining was calculated by dividing the kWh used by the percentage used and multiplying by 100.

This method provides a good estimate of the energy, in kWh, available in the battery, although it still allows for error. The closer the battery is to completely empty, the more accurate the results appear to be.

The last step is to calculate battery degradation by comparing the available energy with the stated capacity (in the Bolt's case, 60 kWh) and any previously calculated and recorded capacities.

By repeating the exercise on a regular basis it is possible to build a consistent and accurate pattern of available energy over time, and by so doing, track the rate that the battery deteriorates.

In Way’s case, the battery capacity at 105,0000 miles was close to 55 kWh, implying the Chevy Bolt's battery had deteriorated 8.3% over that mileage. If the battery was to continue losing capacity at this rate, this particular Bolt would cover close to 500,000 miles before requiring a battery replacement. Not bad at all, for a small EV.