The i3T 2 comes with an included AAA battery, but you can also use a 10440 Li-ion battery with PCB protection (max length 44 mm), which can boost the maximum output up 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. Both soft and heavy activation can be set default mode by simple operation, making it more obey to your will. Compared with the i3T, this 2nd generation gets 31% more battery life, and 71% more runtime in High mode. They optimized the circuit to ensure its surface temperature less than 113*F even during long-time work.