Battery durability testing
This is a summary of a 3 ½ year field-test of an NCR lithium-ion battery. For discussion of our batteries in general refer to discussion 4, “Battery technology”. For 2022 we upgraded from NCR to INR chemistry (greater range) and are in the process of repeating this endurance field-test for these batteries (so the actual data for NCR is not as relevant as it once was). This article does, however, illustrate the test methodology.
Estimates of the service lives of lithium-ion batteries are of necessity based on what manufacturers term “accelerated aging” tests (because new variants of lithium-ion chemistry have not been around long enough to generate “real-time” data from in-service experience). For 3 1/2 years I did all my e-cycling with the same battery, expressly for the purpose of getting real-world data on its performance (i.e., “aging”). During the 3 1/2 years, this battery was charged about 300 times, as it powered the bike through temperatures ranging from -20C (in Ontario) to +40C (in the deserts of the US southwest). Altogether it accumulated 4000+ km of riding.
Measured in bench tests, the energy capacity of this battery was compared with that of when it was new and is shown in the graph below. The area under the curve (V x A.h = Watt-hours) equates to energy delivered by the battery as it is discharged. The test showed an almost negligible reduction in storage capacity…that is, cycling “range” (less than a 3% reduction) … after 3 1/2 years of severe service. The projected lifetime of this battery chemistry greatly exceeded all our expectations, as well as the projections of the manufacturer.