Make sure the spring closest to your PixelWhip's button lines up with the nub of the battery before you screw the flashlight together. If you do not ensure proper alignment, you might deform or bend the spring by accident, causing the PCB spring to lose contact with the battery momentarily - as a result, your PixelWhip may flash red/turn off.
Please note the following is a DIY fix that may void your warranty! Use at your own risk:
You can also try to stretch the spring in the endcap of your PixelWhip if it has become too compressed. To do this, slide your foam grip off the end, and then unscrew the end-cap to access the spring inside. Then, carefully stretch it to make it slightly longer (which may improve contact with the battery, especially when you are fiber wielding). You may also have some luck fixing a deformed PCB spring, but be extra careful not to break or pull the spring off while trying any DIY fixes. Again, the DIY fixes described here (fixing the spring yourself) may void your warranty, so email us at our support address if you don't want to risk this.