I recently got a Nemesis clone and love it. Now I'm using 2 types of 18650 batteries I'm using with it. They are the Efest IMR 18650 2500 mAh 3.7V LI-MN High Drain Rechargeable Battery, Flat Top, Purple, 35 AMPS and the Sony US18650VTC4 2100mAh 3.7V 30A High Drain Hybrid IMR Battery - Button Top with either a Kick2 (haven't tried yet) and the smok Magnet 7A Safety Fuse which I am using. So my question is how does one know when the battery is getting low and needs re-charging before it is too low? The other question is about how long do they last which I know is hard to say but say a minimum amount of time before needing to worry about it? I'm also speaking of freshly charged batteries in both cases. Thanks as the mech. mods are real new to me.