The Efest purple series is an excellent battery for use with mechanical mods.
It is an 18500 size with a 15A 1000mAh capacity battery in a button-top version

Notes:

• Do not over-discharge/overcharge
• Recharge empty batteries ( resting voltage ~3.6V ) as soon as possible. Leaving Li-Ion batteries in a discharged state will incur irreversible damage (capacity/cycle loss )
• Do not short circuit ( will release tremendous current )
• Please do not dispose of it in the fire.

Safe chemistry LiMN means reduced risk of venting with flame or explosion. Due to the safety inherent in IMR-safe chemistry batteries, no protection circuitry is added or built-in. This provides a slightly shorter battery length to fit most mods well. To ensure longevity, allowing the battery to discharge below 2.5V is not recommended.

Due to their inherent safety, IMR cells don’t have a built-in protection circuit. They should never be discharged below 2.5 volts, or cycle life/performance will be reduced. The maximum charge voltage is 4.25 volts.