Charles Ellicott Commentary 2 Chronicles 13:12

"And, behold, God is with us at our head, and his priests with the trumpets of alarm to sound an alarm against you. O children of Israel, fight ye not against Jehovah, the God of your fathers; for ye shall not prosper." — 2 Chronicles 13:12 (ASV)

God himself. — The (true) God. So in 2 Chronicles 13:15.

Literally, and behold there are with us at the head the God and his priests, and the trumpets of alarm to sound alarm against you. (Numbers 31:6.)

The trumpets were “the divinely appointed pledges that God would remember them in war.”

The Syriac gives this verse thus: But you have forsaken him, and gone after dead gods, and worshipped and bowed down to them, and forsaken the Lord God of your fathers; and also you shall not prosper in the world.

Then there is a lacuna extending to 2 Chronicles 13:15.