If it is true that God and Satan are not, have never been, and never will be in a battle, then why do we read in the book of Revelation of a future war in heaven that involves Satan (see Rev. 12:7-9)? That’s a good question, and one that can be answered easily.
Notice that this war will be between Michael and his angels and Satan and his angels. God Himself is not mentioned as being involved in the battle. If He were, the conflict could hardly be described as a war, because God, being all-powerful, could easily squelch any opposition in a moment of time as He has already proven.
Angels, including Michael, are not all-powerful, and thus their conflict with Satan and his angels can be described as a war because there will be some actual conflict for a portion of time. Still, being more powerful, they will overcome Satan and his hordes.
Why would God not become personally involved in this particular battle, leaving it to His angels? I have no idea. Certainly God, being all-knowing, knew that His angels could win the war, and so perhaps He figured there was no need for Him to be involved personally.
I have no doubt that God could have easily and quickly annihilated the wicked Canaanites in the days of Joshua, but He chose to give the task to the Israelites. What God could have done effortlessly in seconds, He required them to do, expending great efforts over a period of months. Perhaps this was more pleasing to God as it required faith on the part of the Israelites. Perhaps that is the reason He will not personally be involved in that future war in heaven. The Bible, however, does not tell us.
Just because there is going to be a war someday in heaven between Michael and his angels and Satan and his angels, that is no reason for us to think that God is not all-powerful—any more than Israel’s battles in Canaan are reason for us to think that God is not all-powerful.