Abstract: Methods, systems, and apparatuses to house cooling fluid for a battery are presented which include a main reservoir configured to house battery cooling fluid, the main reservoir including an overflow opening; and a flexible overflow reservoir coupled to the overflow opening and configured to (1) flexibly expand in volume during inflow of excess battery cooling fluid from the main reservoir through the overflow opening and (2) flexibly contract in volume during outflow of excess battery cooling fluid to the main reservoir through the overflow opening; the flexible overflow reservoir further configured to maintain a substantially same internal pressure during an expanded state or a contracted state of the flexible overflow reservoir.