Tech is the 3rd bar in a characters statistic display area in battle, and can only be seen and used in battle.
It is used for more powerful attacks or buffs then Skill, But it recharges only by using Scream, Eating Donuts or Getting hit/killed.
Its main use is Combo Attacks, Which are powerful attacks that consist of several skills together. To use a combo attack you need 100 Tech.
Mangle's special attack "The Bite of 87" Also needs 100 Tech, and is used to eliminate BB in the final battle of FNAFB 2, Dealing insane amounts of damage.