Two advanced reactors: 2/2 and 96/98. Energy rate - 21 per minute 
Unmount -> mount back in same slots - energy rate - 23 as should be 
This is only on single ship.
Was that an old unused ship by any chance? Unmount -> mount back in same slots - energy rate - 23 as should be This is only on single ship.No, i use it for mining as often as other ships. I thought problem in reactor, so recheck it twice (in SG2 and in SG1), but you know results.
Actually, there is only one way be sure in durability state in SG2 is place it in cargo and attempt repair on station
How equipment's durability losing work...
I think it's all about thrusters (approaching) and not jumping, when it comes to engines. And it's pretty random. Reactors might lose durability as they recharge you, everything else might lose durability on use.Before posting question i made some tests: couple scans of asteroids with just bought used scanner, even mine some asteroids with already broken laser; made thrusters across the system with three new engines, on short distance with 2 minutes cooldown, then few on long distance with 10 minutes cooldown, but any equipment still has 100% durability. Well, then i waited until 20% hull points left and took a trip from Miaplacidus to Tabit 1544 and back to Miaplacidus, BUT still 100% of all engine's durability.