A single AAA battery offers the i3T 2 a max power of 200lm output; 10440 rechargeable li-ion battery (not included) is also supported and can boost the light's max output to 300 lumens. The clip on the i3T 2 is now stuck between the battery cover and the body -- never worry about falling off and it allows for deeper pocket carry. Compared with the i3T, this 2nd generation gets 31% more battery life, and 71% more runtime in High mode. We optimized the circuit to ensure its surface temperature less than 113*F even during long-time work. Size: 3.5in Lenght x 0.59in Dia