abkakar

I am currently working on Flooded VRLA battery. I applied a current profile on the battery in which its SOC moves from 50 % to 80 % SOC range in every cycle. Its a constant profile for 440 hours. But in every new cycle terminal voltage is increasing ( or we can say expanding in both upper and lower side ). Also if we notice the OCV after 30 mints of resting is increasing. Now i need to estimate the SOC of this profile. As the current is same in every cycle but OCV and terminal voltage is increasing , so SOC estimation is different for every next cycle while it should be same as current is same. I would be really thankful if someone help me by telling the reason of this phenomenon. P.S. Battery is placed in a chamber where temperature is maintained at 25 degree centigrade. I am using a BiPolar power supply controlled by computer to provide current to the battery. Voltage is measured by a very accurate sensing circuit.440 hours profile of current and voltage is shown. Also zoomed profiles of first five cycles are shown. In the current graph , positive current means discharging and negative current means charging. Capacity of battery is 90 Ah and 4.5A current pulses are used for 1 hour with 30 mints resting between each pulse.