A Battle computer was a machine intelligence that guided the forces of the Daleks and the Movellans during the Dalek-Movellan War.
With both forces following a logical machine outcome, the war lasted for centuries with not a single shot fired as both sides were equally matched. In order to find an advantage over their enemies, both sides sought an advantage over the other. The Dalek Empire reawakened their creator Davros who would program their computers to provide them an advantage over the Movellans.
The Movellans once discovering this problem demanded that the Doctor program their computers likewise in order to defeat their Dalek foes. (DW: Destiny of the Daleks)