Setup:

Place a mekanism Energy cube, place a Power Monitor, set anything like Emit redstone if >=50 and <=100, just as an example.
So once it is >= 50% it will emit the redstone, great, it works.

Now remove the Energy Cube, and place another one, like a different tier (like an Elite Energy Cube). It stop working, it doesn't detec the block charge level anymore, it only start to detect again if one breaks the monitor and place it again, and set the configuration back.