These are the battery packs (4 little batteries connected together) in a 5 pack. This 5 pack offers the best pricing, though they are still about $10 a pop.
If you turn the laser off between shots and between reloadings, the battery life seems to be reasonable. My experience has been that a battery pack lasts for about 5 hours of actual shooting (and sighting).
Pros: Best pricing quantity
Cons: Still pretty pricey
This review was written in the old system and had content requirements that are different than reviews written today.