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BMS is key for reducing warranty fulfillment costs

Warranty conditions for e-bike batteries always include the guaranteed capacity until the end of the warranty period. Often a maximum (full-equivalent or partial) charge/discharge cycles and more and more conditions to deny warranty in case of deep discharging and/or minimum charge intervals.

The capacity can be determined by a battery analyzer but the other information is stored in the BMS. This article describes the optimal method to test all parameters by dealers.

Measuring the capacity

The only reliable and accurate way is to fully charge the battery with the charger supplied with the battery, followed by discharging to the minimum cell voltage. Battery analyzers may stop charging at default 3.0 V per cell, but the manufacturer may have decided on a higher cut-off voltage (to achieve a higher lifetime at the cost of a smaller capacity). Then they can program the BMS (battery management system) to switch the charging off at a higher voltage. Most battery analyzers allow the user to change the default values.

Capacity factors

The discharge current and internal resistance are important factors in determining the capacity, because the discharge current x internal resistance = voltage drop. Manufacturers may specify the discharge current for warranty purposes, but often do not. If the warranty discharge current is low, the battery will seem to have as higher capacity. An accepted industry standard is 0.7C (C = new capacity in Amp-hours or Ah). For a popular 36V 10 Ah battery this leads to 7A, which also happens to be the nominal load of a Pedelec motor. The higher the internal resistance is, the smaller is the usable capacity. Manufacturers may warrant the maximum internal resistance.

Reading & Interpreting BMS data

A BMS with communication capabilities can be recognized when the discharge connector has more than 3 pins or when the battery has a separate communication connector. One common method to access the BMS data is a stand-alone BMS reader, which displays the content of the BMS. The dealer must then interpret the meaning of the figures, which requires training. The next best method is a BMS that connects to a PC or laptop to interpret the results, either at the dealer or over the phone. But in both cases the dealer must have BMS readers for every brand, or even per model. Even when provided for free, dealers do not like non-standard approaches.

Battery analyzers with BMS Support

When a battery analyzer supports a wide range of batteries with communication capabilities, the interpretation of the data can be done in a uniform way and in accordance with the warranty conditions of the manufacturer. When dealers have this class of battery analyzer –that is also accurate enough and can provide the required discharge current- they can determine warranty eligibility as complete and accurate as a manufacturer or service center can.

Warranty on a distance

When dealers have a battery analyzer with BMS support, this opens the door to involve the e-bike dealer in warranty fulfillment. Currently, Battery Condition Test is the only battery analyzer manufacturer who offers free BMS Support to manufacturers. They designed BMS interfaces for BionX, TranzX, Varta Microbatteries and Contitech (Continental e-bike systems) and more are in preparation. The interpretation of the BMS data for each model is done in the test report, based upon the warranty conditions and texts determined by each individual e-bike manufacturer.

Why not everyone jumps on the boat

Some manufacturers are hesitant to provide a communication interface is because they believe that this would endanger their intellectual property, especially when they used the BMS also to control other e-bike functions. This is not correct, as BMS designers can easily determine which data is allowed to include in the test communication protocol. Many decision makers in the young e-bike industry –understandably- do not have the background to oversee this specialized matter, especially when the BMS was contracted out by them or they were not involved at all. But most are not aware of this great opportunity; this article serves to increase the awareness.

Warranty fulfillment by e-bike dealers

Manufacturers will decide how far they wish to involve dealers and under which conditions. The most economical way (for the manufacturer) is to accept the test report by qualified dealers and authorize the dealer to fulfill the warranty application. This saves high logistic cost (dangerous good surcharge – special packaging) and saves a lot of time and thus a better service to the consumer. In such case the dealer will also be required to provide digital photos of the battery to ensure there is no mechanical damage, whereby the serial number is visible (to compare to the BMS serial number. The battery then goes straight to recycling from the dealer. Another good approach is to accept the report and pick up the replaced batteries combined with a delivery.

Required training by e-bike dealers

Whether or not the dealer will be involved in warranty and regardless of whether batteries with BMS support are being tested it is usually not necessary to be trained in using a battery analyzer as good systems are easy to operate and require no specific knowledge. Training is required for proper understanding of how a battery works and how to communicate the test results. Battery Condition Test developed a 1-day course for this purpose, which will be held in Europe, America and Australia in September, October and November 2015. The course is independent on the battery analyzer brand and can also be followed by dealers who do not own a battery analyzer.

For more information:

E-bike (system) and battery (BMS) manufacturers,
E-bike Dealers in Europe: +31 (0)854444500