DigiCam EC-741

This cell tester works on the same principle as the ZTS testers, checking a cell's voltage under load, with various loads for different chemistries. This little gem, however, is significantly smaller and lighter than even a ZTS Mini, and it doesn't even need batteries to run! Just set the switch to rechargeable or primary and pop a AA/AAA cell into the holder or press a 9V, CR-V3, or 2CR5 battery to the nubs. If the cell or battery has more than 1% capacity remaining, the LEDs will all light up simultaneously for a moment and then deactivate. A couple seconds later, the LEDs will give you a reading of <20% (no LEDs lit) to ~100% (all LEDs lit). That's it!

This is just about the least expensive tester available that actually tests cells in a meaningful way. It's also small, light, and passively powered. I even convinced my supervisor at work to buy one for our work area, and he's been quite satisfied with it. For around $15-20, it's an absolute bargain.