Most commonly known as 9V or 9 Volt battery, the 1604 is actually a battery pack. Within are seperate battery cells assembled to have a rating of 9V total. This means that any chemistry of 9V can be used and should only be influenced by capacity and cost. Lithium has a higher capacity (mAh) compared to alkaline, giving it a longer run time. The rechargable versions (Ni-MH and Li-ion) have lower capacity but can be recharged up to a thousand times, costing less in the long run as they replace hundreds of primary (alkaline and lithium) batteries.