A battery system includes a plurality of battery cells abutting one another to form a battery cell stack. An optical communication link is connected to each of the plurality of battery cells. A battery management system (BMS) connected to the optical communication link configured and adapted to receive information from the optical communication link. A method of controlling heat transfer in a battery system includes monitoring at least one characteristic of at least one battery cell of a plurality of battery cells with at least one sensor, and sending information from the at least one sensor to a battery management system (BMS) with an optical communication link. The optical communication link is connected to each of the plurality of battery cells. The method includes selectively varying a fluid circulation rate in the battery system with the BMS depending on the at least one characteristic.