Pure voltage wise a LiPo battery should be stored (or returned back to within a couple days) 3,7-3,8V/cell (that's approx 30-60% in the app)... this is still valid.
Keeping them in a too high charge state will speed up the electrolyte decomposition which release gases, so the battery can start to swell & the internal resistance will increase making the battery very prone to major voltage drops when put under amp draw.
Keeping them too low will first risk a shutdown of the BMS chip (mainly make the battery not take charge anymore & usually it's nearly impossible to "wake" that BMS up again without special equipment)... then secondly the battery might self discharge under 3V/cell & there the cells will be permanently damaged.
One charge cycle is from wherever it is percentage wise, the discharged... & then returned to the same "wherever percentage"... so, from 100% down to 0% & charged up to 100% = 1 charge cycle.
A M3E battery isn't anything special... it's a LiPo with a model specific outer plastic casing... depending on age, use & care a LiPo should perform "good" up to 200-300 cycles... but the capacity it can store will slowly degrade over use & age. So not impossible that a LiPo can be dead with only 1 cycle if it have been stored wrongly & are very old.