I almost never boil 2 cups with my tea light, usually 10-12 ounces. If it's really windy I may not get a boil, but the water is still hot enough. If I absolutely needed a boil every time I would use something else.

You can find larger tea lights. I have some from Whole Foods that hold around 3/4 oz of alcohol. Someone posted on here a while back about using a metal "wash basin" found at Hobby Lobby in the dollhouse furniture section. I did check that out and it looked like it would work if I needed something to hold more alcohol.