Makes it very fast and easy to check overall and per-cell battery voltage. Comes in super handy if you’ve got multiple batteries to check and a charger with a cumbersome interface. The buzzers are obnoxiously loud, though. I peeled the instructions and foam off the back and used an xacto knife to cut the long thin trace powering the buzzer. Much nicer to use now, would recommend.

Bought as a small and inexpensive battery checker that looked handy to keep in your pocket, and worked when received, but it has an almost painfully loud beep, so was rarely used. The instructions on the back say that the low voltage alarm is adjustable, "OFF 2.7 - 3.8" But after adjusting, the checker failed and is no longer usable. The checker now displays the voltage of all cells and the first cell, but can no longer read the voltage of additional cells after the first cell in a 2S, 3S, 4S, or 6S pack; it beeps loudly while indicating that cells 2 and up have 0.0 or 0.5 volts.