V.V. Pechenko - Leading Engineer, JSC «Concern «Automation». E-mail: 5309721@mail.ru

The state-of-charge is often needed to be calculated in different periods of time for devices having rechargeable batteries and power supplies combined. Mathematic methods based on amperage and voltage measurement are often used. Error measurement is important as such methods are naturally inaccurate. This paper describes mathematic model of rechargeable battery using Kalman filter calculation. Within this method, the battery state-of-charge is a part of battery state and so Kalman filtering allows automatic gathering of state-of-charge calculation error.