2 Chronicles 18:29-3

(1 Kings 22:29-37). The Death of Ahab at Ramoth-Gilead

29. I will disguise myself Ahab's proposal is that he himself (disguised) should take part in the fighting, and that Jehoshaphat in royal robes should remain in the rear. Thus Ahab would be doubly protected, i.e. by his disguise and by the chance that Jehoshaphat would be mistaken for him, while Jehoshaphat In the rear would run no risk.

put thou on thy robes Render, be clothed in thy robes, i.e. do not put on thy armour, but keep out of the fighting.

and they went to the battle 1 Kin. (more correctly) and he(Ahab) went into the battle(so LXX. here).