You just set up your equipment for the first dive of your vacation in Saint Somewhere, as you press the activation button on your dive computer it goes through the diagnostic screen and what do you see the "Low Batt" icon appears. The worst thing that can happen on a tropical vacation has just happen No Dive Computer. Don't leave on a vacation without spare batteries, why ruin a great holiday because of a few dollars in batteries. This kit works with the Cressi Leonardo/Giotto Dive Computers. Included with the kit are a 3.0 Volt Lithium CR2430 Battery, Battery Hatch O-Ring, and a Small-Tube of O-Ring Lubricant. Kit is Factory-Approved and makes a great Save-a-Dive Kit item. Always pack some spares, don't forget your Dive Light needs some too!