It's a portable base. You can go behind your tower, use it, and go back to battle.
Cooldown? Literaly, whenever you need it.
A.k.a overpowered, lame, game-breaking, must-have, zomfg... etc.
Best fix is to lower the amount it regenerates. By 75%.
Such a cheap item should be helpful, not dominant over all the other items combined and map possition.