The history of the events was thus: Chizkiah and Achav got together to go to war. But before they went Achav called all his prophets to hear what they had to say. (Why would he do this, unless they had been proven accurate on every other occasion that he consulted with them?)
They all came and said he will win the war. Chizkiah then asked:
"Is there no prophet of God here?"
Achav said: "There is one; Michaihu is his name. and I hate him.
"Why is that?"
"Because he speaks only badly of me all the time."
"Call him and let's hear hat he has to say."
He came and said you will win the war. Achav said to him how many times do I have to tell you to say in prophecy only the truth in Gods name?
The Michaihu said that he would be killed in battle.
Achav then commanded he be put into prison until his return.
Michaihu said "If you return alive, then I am not a prophet of God."
Achav was killed. He had been fooled because everything else the prophets of the Baal had said had always turned out right.