The US Army has recently transitioned to using “maintenance free” batteries in its ground vehicles to increase the over-all vehicle readiness. Using lead-calcium alloy grids in place of the “reduced maintenance” design decreases water loss. This loss of water is known to be a measure of the battery self discharge. In this study, the charging of SLI batteries was examined over a range of operating temperatures as a means for characterizing the self-discharge rate as a function of battery voltage and temperature. The battery response was modeled analytically. Current activities are directed toward achieving a better description of the battery self-discharge over extreme environmental conditions.