How to Know When Your Quadcopter Battery is Almost Dead
Here's my current solution to knowing when the LiPo battery on an RC airplane or quadcopter is about to die. It's only my current solution because I'm destined to build a custom solution, but this is simple and cheap and it works really well.
The solution is this LiPo voltage checker and warning buzzer.
Just connect this up to your 1-6 cell LiPo battery balancing cable while in flight and when the voltage on an individual cell drops below a configurable value, it will emit this loud and annoying beep that's hard not to notice. This is my indication I've got about a minute to land before my quadcopter lands itself rather ungracefully.