Do your Spellcasters win or lose their duels?

It kind of depends for my spell casters. All of them are still kind of low, because I am a rotational player, and slowly level them up.
I noticed that when my spell casters are super tired, or at risk of overcharging they tend to lose. However, if both Sims are fine, it is a toss up between the two.
In one family, the mother was tired, and went up against her daughter, her daughter won that duel. However, the mother was fine when she wen up against another sim, and she won that duel.
I have had mixed outcomes with the magic duels.

A couple of my casters have won several of their duels while their overcharged meter was half full. There is no set way to win a duel. From my experience with this, it doesn't matter if you have your caster practice all the time or not or if they are the most powerful caster in your game or not. It does not guarantee that your caster will win a duel every time. And it also does not matter how full their overcharged meter is, it still doesn't guarantee that they'll win every duel.