The objective of my Diploma thesis is to design and build an electrical motor cycle. To complete this task first of all we have to specify the main parts of the system. Just after this and the knowledge of the relevant Hungarian regulations can be chosen the most important module, the donor vehicle. Since every rebuilding needs its own base, my project has one too. It is RIEJU RS1 motorcycle made in 1996 in Spain. The motorcycle originally was powered by an 50 cc internal-combustion engine. This engine was replaced by a 2 kW nominal power electrical engine. Choosing the engine determines the main parameters of the other system components. The 2 kW power load is just a nominal value but starting or accelerating can be required more power. The maximum power load is 5 kW. The system voltage is determined by the engine (48 V). To reach the maximum power is required 100-110 A besides 48V. This two value are dominated by the view of the batteries and by the motor-controller. In the view of the batteries the current and the voltage determine the maximum number of cells, and the minimum value of the capacity. In the case of the motor-controller these two value determine the current band of the controller and the input voltage range. I constructed a battery pack with 16 piece of 40 Ah, 3.2 V nominal voltage, LIFEPO4 chemistry, Thunder-Sky battery cells based on the specification. The available energy reaches the engine through the KEB72801X motor-controller, made by Kelly Controls. The list of the modules is not complete yet. These modules constitute a minimal system. This construction can be damaged permanently after some recharges or even the first complete discharge. I designed and built an electronic system to protect the batteries from the overcharging and discharging. These electronics can be used to avoid the overcharge and the deep discharge, but – for the sake of applicability - they are not able to turn of the vehicle. To avoid the deep discharging one module is responsible to process the values, measured by the batteries control modules, and display them on the central display if it requires. Of course the driver needs to be informed about the states of the periphery’s. On the display can be shown all of those information that are related to the driving such as index, headlight, distance and so on. All of the electronics which placed into the vehicle can communicate with each other using the via RS485, synchronized by an on-board electronic can be found behind the central display. There is a data logger module connected to the network. This module logs every piece of information about the vehicle such as cells' voltage, remained charge and so on and save them into SD card. These data can be used to determine the inside resistance of the batteries. Knowing these values we can easily find out the current state of our batteries. The logging starts right after that the vehicle was started. Once the logging started up a file have been generated automatically with name of the current date. All data get into this file line by line. This measurement is completely automatic, user intervention is not required neither at the starting nor at the stopping.