The paper focuses on the charging of LiFePO batteries with big output voltage. This voltage is necessary to feed a frequency inverter circuit with approx. output of 7.5 kW. This is a part of the solution applied during the Pre-seed project solved in the past at VSB - TUO Ostrava. Due to the unavailability of standard chargers, we provide a solution based on the Siemens 6RA80 controlled rectifier.