Safe chemistry LiMN reduces the risk of venting with flame or explosion. With IMR-safe chemistry batteries, no added or built-in protection circuitry exists, resulting in a slightly shorter battery length that better fits most mods.

To maintain longevity, it’s advisable not to allow the battery to discharge below 2.5V.
Efest IMR 18500 LiMn 1100mAh Battery – Flat Top

Due to their inherent safety, IMR cells lack built-in protection circuitry, so discharging them below 2.5 volts can reduce cycle life and performance. The maximum charge voltage is 4.25 volts.