I use 4 batteries, 36 volts. I heat the water with my coffee maker and pour it in the jar at hot coffee temperature. Whatever Rival heats it to is perfect for drinking without burning the tongue. But I never stuck a thermometer in it. There are You Tube videos that say to boil the water and that will make it golden. But it's too hot to handle the jar and if you spill some it's hot when it splashes, so I prefer hot coffee temperature.