Stacks of Load 'n' Splode last 14 seconds, or twice the duration of a kill skill. However, each stack decays individually, meaning that when a stack is gained, that stack will be lost after 14 seconds. Thus, is it impossible to maintain 5 stacks for more than a few seconds at a time without repeatedly reloading, because the older stacks will disappear.
Load 'n' Splode increases the damage of several of Claptrap's other skills, including Start with a Bang and Repulsive.
Load 'n' Splode's damage bonus is multiplicative, meaning that other relevant damage bonuses will be multiplied with the current stack bonus instead of added. With grenade or gun damage bonuses, this can allow Load 'n' Splode to grant huge increases to damage output.