I believe improperly and/or overcharged
batteries increase the risk of failure. You should never charge batteries on a device that does not support automatic shutdown at full charge, and never inside the mod. The heat places undue stress on the control board.
Be mindful of your environment as well. These devices are soldered with lead-free (RoHS) solder. Lead-free solder is non-pliable, cracking easily when subjected to temperature extremes. Lead was added to solder for stability. Those experiencing sub-zero winters may want to deem your mech devices as seasonal... i.e. Winter mods.