The Future is here! Meet the MAX 400 Variable Voltage Battery. MAX has a ten second preheat and four levels from 3.3V to 4.2V.
Small and sleek and priced to sell at $15.
Plus Max turns on and off with no external buttons. Just tap the pen into the palm of your hand five times and turn it on. Two taps to pre-heat. Three taps to change level. Then inhale and enjoy the autodraw feature. And the lighted end lets you know where you are. No strings on me!