Summary

Electric cars are better for the environment in general and certainly in terms of local air pollution. But the benefits are limited if the cars will only last ten years, which is the expected life of the battery packs in the typical EV on our roads today. Blue Cars performed our first battery pack swap for a Nissan Leaf in 2016 and have completed dozens more since then, but the supply of good used packs from wrecks is constrained and uncertain. In 2017, following several failed attempts to buy new modules and/or packs from Nissan, we started looking into assembling our own replacement modules here in New Zealand.

The illustration below gives a rough idea of what we were thinking – buy new battery cells and use these to assemble new battery modules, to then rebuild existing battery packs leaving all other pack components unchanged (generally only the battery cells degrade and all other components are still in great condition).

Image 1 – Our concept design in a nutshell.

Image 2 – Prototype module installed in a Nissan Leaf battery pack for testing.

Results

Four types of 18650 cell were tested and found suitable for our application. All offer a significant capacity increase over the 24kWh Nissan battery of between 50% to 80%. A prototype module was constructed and successfully bench and vehicle tested. While further work is required to develop this successful prototype into a viable production-ready product, our experiments have proven that we can build an upgraded Nissan Leaf battery that should have greater than 200 km of range.

Image 3 – Measured capacity of our prototype module compared to various benchmarks.