Mortar Battery is the final upgrade of the Mortar Tower in BTD4, right after the Bloon Buster. The Mortar Battery is the same as the Mortar Tower except for the fact that it attacks three times as fast. They cause serious bloon damage for anything except for zebras and Black Bloons, although not as effective as MOAB Maulers, making MOAB Maulers the better choice. It is unlocked at Rank 23 in BTD4.