LiPo batteries need looking after if you want to get the most use out of them. One of the most common mistakes users make is running their batteries down too low. If LiPo cells drop below ~3.2V then it can't be safely recharged and your charger will just say 'nope'. In order to prevent that during use, you can use a voltmeter which look cool but require vigilance. These little alarms plug into the battery balance lead and monitor the voltage of each cell as you play. Plug it in when you install the battery in the blaster and it will bleep and flash green to show you everything is cool. If the battery becomes too low during play, this little doodad will flash red and bleep like an alarm clock, signifying that it's time to put it on charge. The LiPo alarm is the smallest physical device of it's type that we could find so it'll fit in most blasters. Notes for use: The alarm will work with both 2S and 3S LiPos. It can take a few attempts to get the plug orientation correct so try it a few different ways if it doesn't work straight away. The alarm itself will draw a very small amount of current so if you leave your battery alone for some time (transport or storage), you should unplug the alarm to prevent it draining the battery.