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Scientific Research Proves: 8-Year Warranty on E-Bike Batteries Possible


MARYLAND, USA – CALCE, the electronics/lithium-ion test laboratory of the University of Maryland, USA, conducted a study and practical tests on lithium-ion cells. They proved that 8-year warranty terms for e-bike batteries are possible by reducing charge/discharge levels. For making that possible automatically an universal ‘Battery Saver’ is being developed.

Scientific Research Proves: 8-Year Warranty on E-Bike Batteries Possible
For enabling prolonged lifespan, automated charging/discharging to favourable levels is needed. For that ‘E-Bike Battery Saver’ is being developed. – Photo Bike Europe

The test by CALCE were carried out at the request of e-bike battery consultant James Post. Aim of the study and tests was to obtain scientific substantiation that a reduced SoC (charge/discharge) minimizes range degradation and thus increases service life. It confirms previous research and daily practice experiences throughout the electric vehicle industry showing that a reduced SoC of typically 20 – 80% enables manufacturers to offer an 8-year pro rata guarantee to end users.

Research results

As the scientific article, published in the Elsevier publication for scientists ‘Journal for Power Sources’ (reference: Journal of Power Sources 327 (2016) 394-400), is not that easy to understand for everyone, James Post has put together a summary of the results, which has been approved by Professor Pecht, CALCE director. The research proves that:

  • At a 20-80% charging/discharging range, the service life is about twice as long than at the 0-100% range. Loading up to 80% is the dominant factor for a prolonged life time of e-bike batteries.
  • Even better results are achieved by charging up to only 60%, but because reducing the range even more this it is not practical, so we would not call it a formal recommendation.
  • Although not clear from these tests, from previous research and experience in other electric vehicle sectors is known that it is beneficial for the lifespan to keep discharging above 20% battery capacity.
  • When not in use, charging during storage up to 50% is beneficial as long as the battery is being charged before reaching 20% of its capacity. This is highly dependent on self-discharge, which differs considerably between various batteries, mainly due to electronics design.
  • The impedance and internal resistance are slightly negatively influenced by full charging.

Research recommendations

  1. Just as with electric cars, charging e-bike batteries up to 80% is advantageous, if the range is still acceptable compared to the range at 100%.
  2. Storage between 30% and 50% charge/discharge levels is very favourable compared to 80 – 100% which is daily practice with regular charging.

The CALCE study and tests conclusion is that storage and use on the basis of these recommendations can at least double the lifespan of e-bike batteries.

E-Bike Battery Saver

When storaging e-bike batteries as well as in daily use optimal charge/discharge levels are not likely to be taken into account. To enable a doubling of the life span of e-bike batteries automated charging/discharging to the favourable levels is needed. For that a universal solution will soon be introduced. It’s named the “E-Bike Battery Saver”. This Saver is connected between the charger and the battery, and the user selects the levels to which she/he wants to charge. This can be in a low-power mode (usually OK at 65 – 80%) and if necessary (occasionally – for a longer trip) 100%. During winter storage the battery is automatically kept at a 40 – 50% charge.

This functionality should actually best be built into the battery, so the additional costs are small. But a built-in version does require a re-design of the battery management system. Because extending battery life seems no priority and re-designing is not customary, this probably will take years.

Recently a 2nd prototype of the E-Bike Battery Saver has been developed. 25 final prototypes will be produced next February. Thereafter the prototypes first will be sent to CALCE for an evaluation of reliability and lifespan. Then they are presented to dealers and other parties willing to test them. The E-Bike Battery Saver is expected to become available end of April, 2018.

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