I'm fighting Elesa's Zebstrika with my lv.30 Dewott and I keep on healing him until Zebstrika runs out of pp for volt switch but he keeps on using volt switch.
Yes Gym Leader's Pokemon do run out of PP, but Volt Switch has 20 PP and Elesa has 3 Pokemon that know it.
You best have a lot of potions if you want to stall out Elesa's Volt Switch.
Or get a Sandile.
I'm 99% sure that they do run out of PP, I remember a Pokemon having to use Struggle on me. You must have miscounted the PP.
They do have PP. Source: Experience I hope this helps! -Jellohamster
They will run out of PP eventually, but that's a waste of time and money. My suggestion: level a sand shrew up to level 22 and laugh at how easy it dominates her team