Don't throw away Good batteries! Test them first. The portable battery tester by La Crosse Technology tests one battery at a time. Test your rechargeable or alkaline batteries in the following sizes: AAA, AA, C, D, N and 3V lithium button cell batteries, also side contacts for 9V batteries. The compact size allows you to carry the tester with you on the go in a purse, camera bag, luggage or backpack. Simple operation: Select battery voltage, insert battery according to polarity, pressing tester to make contact you can read battery strength on LCD.