One of quad engines still running while on battery

[tobias]

It sounds like a broken M4 mosfet since it worked before. Have you tried measuring the resistance like described in this post?

[tomdeb]

Hi Tobias,

blue-green resistance is 100ohm and blue-yellow is 10ohm, not 10k ohm as should be. So what is broken?

[tobias]

It is probably the mosfet that is broken then. It is not too hard to exchange if you have some soldering skills.