Transformers: War Within Pocket Paperback, Volume 1

Eons ago on Cybertron, the Great War is in its early stages, with the vicious Megatron cutting a swath through the ranks of the Autobots. When the previous Prime is killed, the High Council chooses a common data entry bot to step up and become the new leader: Optimus Prime, but not everyone is happy with the new choice, as his initial command decision is to surrender Cybertron to the Decepticons. Meanwhile, Megatron works to activate planetary scale engines which could remake the face of Cybertron. He needs one thing to power them... and Optimus Prime has it.
Dreamwave Productions; Pocket edition (2003)