Legal Question in Family Law in California

"I will win?" - Wow, there are really no "winners" as taking a child away from a parent is never good for the child. Both parents are to be in the child's life.

Otherwise what does a DUI have to do with his parenting skills? Was the kid in the car or something? Does he drink when alone with the child?

The court has the responsibility to ensure the children's safety. If your ex has a drinking problem and it impairs his ability to parent, then go back to court on a motion requesting that he participate in appropriate sobriety programs and request supervised visitation in the interim.

You have received two very good answers. I would just add that one of the best ways to "lose" a custody case is to be too aggressive and come across as trying to impair the child's relationship with the other parent. Make sure that what you go in asking for is OBJECTIVELY in the child's best interest, not just in YOUR "I hate my ex and they are a dirt ball who I want to punish for being a drinker" opinion of the child's best interest.