Bests & Worsts Reviews from Amazon

This product uses batteries, 3 LR1130 coin cells to be specific (L=alkaline single use non rechargeable ~1.5v, R=round, 11=11mm diameter, 30=3.0mm tall). Pushing the "on/off" switch forward uses these built in batteries and disconnects the crank lever thing, pulling the switch back swaps to hand power and takes the batteries out of the loop. The batteries cannot be charged and squeezing while its on battery does nothing. If you squeeze the lever with the switch "off" (back) it does run the lights but much dimmer and you need to squeeze more than once per second to keep it on. Changing the batteries for fresh ones is technically possible but it would be cheaper and faster to built your own flash light out of duct tape and 3 AA batteries. It produces enough light to not run in to walls and read with eye strain but it would be unpleasant to use for more than a few seconds. I never had any intention of using this as a light and instead am using it as a demo generator, and it gets that job done at a very low price. The remainder of this review is technical data if you are planning on using this for an electronics science project. The crank outputs unrectified AC power that varies with crank speed. Max performance appears to be around 3V rms open circuit, 80mA rms closed circuit, and runs around 300 Hz. The circuit is 2 ~3v white LEDs connected in parallel with one lead connected permanently to the generator and battery and the other connected to common of a spdt slide switch that connects to battery or generator. On battery the LEDs are fed around 4.5 volts and are pretty bright. The generator outputs a max of 3V rms which is 4.3v peak, but it's LEDs on vanilla AC so they're flickering and are off most of the time. This means they are at <50% the brightness of the straight DC from the batteries. The flickering is at 300Hz so its not visible to human eyes without tricks. You can wave any light and it leaves a trail behind it visible to your eyes or a camera. On battery it leaves a solid trail, on manual power it leaves a dashed trail due to the flicker.