Just experienced the battery drop to 4% (happens always now when battery is <15% on a call ) but despite having applied (strictly following) the recipe (only diff: min=3%, max=5%), it didn't kick in.
After the call (battery still on 4%), I opened PM and the rule appeared as active (blue bar). Opened it and hit "Test" and only then battery level refreshed.
Any ideas on this?

Also wouldn't it make sense to put a 2nd condition "Charging state > Not charging"? At least it can't hurt, right?