A - Accumulator capacity
The capacity, i.e. the energy content, of a rechargeable battery is in most cases indicated in watt-hours (Wh) in the technical specifications of a pedelec. The higher the value, the bigger is the amount of energy made available by the battery to the motor and the larger is the range per charging. Everyone who makes long tours, needs a big amount of capacity. Everyone who cycles short trails, can recharge at home and can manage with a smaller battery (lower in price and weight). Caution: Instead of indicating the capacity in Wh, some manufacturers indicate the charge in ampere-hours (Ah) and the voltage in Volt (24 or 36 V). If you want to compare, simply multiply the charge with the voltage and you will get the capacity in Wh.
B - Batterie management system
The battery management system (BMS) controls and regulates all processes inside the rechargeable battery. During the ride the system ensures the even discharge of the cells and prevents the system from becoming too hot and too high currents from flowing out. During charging the BMS controls that all cells are charged evenly and that no cells suffer from overheating or overcharging.
A good BMS can nearly double the service life of an accumulator and significantly increase the performance and range of the entire pedelec.
A particularly important point: the temperature control. Heat does not only make the cells wear down faster, it can even result in a self-ignition of the rechargeable battery in an extreme case. During long or especially steep uphill climbs the BMS switches off the motor, as soon as a critical point is reached. Although such pauses are annoying during the tour, they protect the rechargeable battery from failure due to excessive heat and the rider possibly from injuries. The quality of the BMS cannot be recognized from the battery, but can be concluded from a few details: A comprehensive connector system, for example, is an indication for the fact that the manufacturer gave thought to the battery and its control. A precise battery charge status and range indication on the display would neither be possible without BMS. If there is only a small control unit with a switch on/off button and a few light-emitting diodes, it is most probable that the BMS is not very sophisticated.
D - Don’ts
Don’t let the battery fall and don’t clean the pedelec by using a sharp water jet or even a high-pressure cleaner. Water could penetrate and affect the electric components; an electric short-circuit is no fun. However, it can become really dangerous when you tinker about with the battery.
Don’t drill a rechargeable battery, don’t clamp anything to it and don’t try to open it, even if you don’t need it any longer.
In addition, accumulators without battery management system don’t forgive the short-circuiting between the positive and negative pole with a metal object (key) or moisture and sett off an uncontrollable reaction.
An absolutely forbidden thing is to charge the rechargeable battery in the open with moist weather, rain or in bright sunlight.
F - Future
State-of-the-art lithium-ion accumulators are already by far better and lighter than former nickel-cadmium and lead-acid accumulators. As with lithium already the third lightest atom is used for the chemical processes, the potential of reducing the accumulator weight is pretty much exhausted. New accumulator technologies are being developed, but a higher performance still means a heavier weight and due to the higher energy density also an increased risk.
Author: Dirk Zedler