Albert Barnes Commentary 1 Samuel 13:5

"And the Philistines assembled themselves together to fight with Israel, thirty thousand chariots, and six thousand horsemen, and people as the sand which is on the sea-shore in multitude: and they came up, and encamped in Michmash, eastward of Beth-aven." — 1 Samuel 13:5 (ASV)

Thirty thousand chariots - This is probably a copyist’s mistake for 300. (Compare 1 Chronicles 18:4 with 2 Samuel 8:4 for a similar numerical variation.)

Eastward from Bethaven - This means “to the east of Bethaven,” which lay “on the east side of Bethel” (Joshua 7:2). Bethaven (thought to be the same as Deir Diwan) was located between Bethel and Michmash, which Saul had evacuated.