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E-bike battery Warranty texts for BMS data

For senior managers of e-bike (system) & battery manufacturers/importers

Battery Condition Test offers implementation of BMS to e-bike manufacturers or their suppliers. R & D costs are not charged when the manufacturer commits to recommend BCT’s battery analyzers to their (OEM’s) dealers, BCT considers the BMS suitable and the scale justifies this.

To perform the BMS implementation BCT needs a working battery for each (different) BMS, 2 contra-connectors (that fit the discharge connector on the battery). Furthermore the communication protocol and contact information of an engineer who understands the BMS well. Then, both a listing of which BMS data (and their locations) are required by the manufacturer and which data are to be used for inclusion in the test reports (by dealers) and any required text interpretations.

This article provides example texts for common warranty exclusions and also serves as a useful check-list for manufacturers to verify if their warranty conditions (and BMS) are adequate enough.

BMS parameterValueExclusion conditionsExample text

Cycle count: 540 >=500 (100% equivalent) The cycle count of this battery is 540. According to [your name]’s warranty conditions this is higher than the warranted number of 500.
Battery capacity: 69% >= 65% (define Wh or Ah) The capacity of this battery is 69% of new
Usage days: 680 days < 730 days This battery has been used for 680 days.
Deep discharge: 25.2V-25.8V 36d.
27V-28V >30 days
26V-27V >15 days
23.6V-26.1V > 93 days no charge
>3 days This battery was not charged during more than 3 days and discharged to 23.6V.
According to [your name]’s warranty conditions this is a violation of the warranty condition: “When the battery has not been charged for more than 3 days and has a voltage thereafter of less than 26.0V, the warranty will be denied because of battery mistreatment”

Note: The values used as examples are not a recommendation; just to explain the mechanism, but we do recommend to use such criteria instead of conditions like “charge at least every x months” and “minimum y days per year at the charger”.

Warranty status: Denied (@ Dealer fulfillment) will (option: likely) be denied (@ Service center)

(if granted): Granted, provided the battery has no mechanical damage or opened battery case (@ Dealer fulfillment)

Provided the battery has no mechanical damage or opened battery case, warranty may be granted. The battery will be sent to the manufacturer’s service center for warranty judgement. (@ Service center). This will take approximately x to y weeks.

Warranty Tips: 1) Consider including a pro-rata condition in your warranty condition. It saves a lot without being unreasonable (much better than a meager warranty period of 1 year)

Example text: The battery with granted warranty will be replaced free of charge, within x months from date of original purchase. After x months, [your name] will charge 1.6% of the then current battery retail price for each:

  • month or part thereof since the day of purchase OR
  • each xxx charge/discharge cycles

The higher of the two will apply. This reasonable arrangement is based upon a normal service life of 5 years and yyy (number of cycles you warrant divided by 60) charge/discharge cycles.

When you implement this, it is economically feasible to increase the warranty period substantially (e.g. 5 years), which is an important marketing argument.

2) In your next BMS Update, consider to reduce the cut-off discharge to 10-20% and when the user wants to use the remaining let them activate a “reserve” function and apply a penalty (to be applied on the % of new that you warrant). Also consider to reduce the standard charge % to 80-90 (to change to 100% on the display) and ideally implement a storage mode, whereby the charger can stay connected and the BMS keeps the SoC at 50%. Our partner (in the BBMS Group) CALCE (test lab University of Maryland) tested cycle life comparing charging to 50% instead of 100% and discharging to 50% instead of 100%. 50% and 80% and 50% and 20% respectively is not a big difference: The essence is to keep the battery as much as possible out of the stress area (anode/cathode oxidation increases internal resistance).

BMS Charge Control may not be easy, but very worthwhile.

We learned this policy from the EV industry, who have no problem with 7 or 8 years warranty, in combination with a pro-rata condition (and better testing…).

3) When your BMS cannot display the (100% equivalent) cycle count, instruct the designer to implement this. E-bikes are getting popular with couriers, pizza delivery… When your BMS cannot display the number of “used days” and “deep discharge” it could be overseen or not specified, but more likely the BMS does not have a “real-time clock” or RTC. By saving less than 1 Euro you cannot check the actual date of first usage. Limiting the storage period until first use to i.e. 1 year is not very elegant and is in your disadvantage in case of false receipts, while consumers forget warranty registration.

Deep discharging is the most common reason for unjust warranty claims.

4) Make sure that your batteries are well tested and on the cell level before shipment. Some BMS’s are unable to recognize individual (paralleled) cell voltages and that means weak cells in the pack are NOT recognized: a substantial difference in warranty claims!