Gruber Motor Company, a Tesla service provider with particular focus on the original Roadster, has released detailed information on how the battery packs in those cars are beginning to reach their end of life. According to the company, this info can teach us the symptoms to expect when multi-cell battery packs in the many long-range EVs that came after the Roadster begin to reach their end of life.

The video published on Gruber's YouTube channel explains Roadsters with batteries reaching their end of life will experience a significant decrease in power when their packs begin to fail, being unable to exceed 60 miles per hour, safely merge onto a highway, or even go up hills. The symptoms are subtle at first, with what one affected owner describes as a "squishy pedal feel," but then increase quickly, eventually rendering the car undriveable.

original red tesla roadster

These findings, though, come from an unexpected source. Gruber has discovered that while Roadsters with their original 200-mile-range battery packs are still healthy, cars fitted with the upgraded 400-mile-range pack that Tesla began offering in 2016 are the ones starting to fail.

The very first Tesla Roadsters were sold back in 2008 and are now 15 years old. Gruber cites the automaker's original Chief Technology Officer, JB Straubel, as claiming the expected lifespan of those original first-generation multi-cell battery packs was 10 years. However, Straubel himself, who owns one of the earliest Roadsters, remarked publicly last year he's surprised to report his car is still going strong, and he has revised his estimate of the original pack's lifespan up to 15 years. Gruber's own data supports this, with the company reporting that most of the Roadsters it services with the original 200-mile-range battery pack are still healthy with no signs of slowing down.

In 2016, Tesla began offering Roadster owners a larger, upgraded battery pack. The upgraded packs cost an eye-watering $32,000 (approx. £26,200) but were claimed to double the Roadster's range to 400 miles and extend their lifespan. These packs were fitted with upgraded 3.2 amp-hour 18650 cells compared to the 2.2 amp-hour cells used in the original packs. Despite the promise of a longer lifespan, these upgraded packs are the ones now failing. 

Gruber began investigating the upgraded packs when it received two separate Roadsters for service, both with the upgraded battery packs, that were exhibiting identical symptoms its techs had never seen before. After a lengthy and technical investigation, Gruber concluded a "cell quality issue" was the root cause of the packs' failure. Without final corroboration from Tesla, they theorise the upgraded packs sold between 2016 and 2019 were produced in the same production run and may deteriorate like this regardless of whether they're frequently in use or sitting in a garage. Gruber states these packs never reached their promised full range of 400 miles either, eventually settling around a maximum range of 200 miles.

The data gathered from Gruber's investigation has ramifications beyond Roadsters with the upgraded battery pack. The Tesla Model S that followed the Roadster uses the same 18650 cells. This data can also teach every EV owner how to identify if their battery pack is reaching its end of life. 

Gruber has shared its findings with Tesla. It's even delivered an affected Roadster to one of the automaker's service centres for further tests to corroborate its findings. The company reports Tesla's Roadster Engineering team is working closely with them now to find a solution.