The electrical power system comprises of the battery management system (BMS) which is an electronic control system for the lithium battery cells and the battery pack which is a key enabling system component in electric motorcycles as shown in figure 1 (page 2). Low-cost lithium batteries cells with higher power densities and improved power factors have changed the way power is used and stored onboard an electric motorbike making them suited for mobile applications [8]. When choosing lithium battery cells, the amount of energy storage required, the rating of the motor and power densities needs to be considered. An appropriate number of series and parallel lithium battery cells matching the motor rating with respect to the maximum voltage allowed by the relevant electric motorbike racing competitions are chosen. For example, MotoE regulations have battery voltage limitations of +/- 300V.

Lithium battery cells have a very non-linear charge/discharge curve making them relatively difficult to manage [8]. For a lead acid battery, measuring its voltage is the easiest way to tell how charged it is and from that data, the state of charge can be worked out. With a lithium-ion battery, it is slightly difficult to work out making it very hard to tell the state of charge of a cell as the voltage relative to the state of charge is very flat around 60% of the charge/discharge curve with sharp inflections at both ends [8]. This makes it relatively easy to cause permanent damage by both over and undercharging the cell and damaged cells can overheat and get into a thermal runaway condition [8]. This is where the BMS plays a crucial role in managing risk and ensuring safety.

The BMS accurately reports the state of charge of the battery pack and monitors the cells detecting any problems to ensure that the pack can be safely shut down when needed. The BMS consists of several separate circuit boards typically such as module control units or MCUs which will monitor the voltage of a small group of cells or individual cells very accurately in the battery. The MCU will also include some temperature measurements to monitor inside of the battery pack and possibly the individual cells linking up to a master BMS module which will combine data from all the slave MCUs measuring overall current flow in and out of the battery pack. With this information, it can work out what the battery state of charge is and reported to the driver via a display or warning light(s) [8].