Yes Pete 3 V is fine .thats what the elements are designed to run with.
youl find resistance of heating coils to be about 2.6- 3 ohms so giving a current of about 1 amp . (So approx 3 watts of power will be used)
It's just that madogg decided he wanted to get much more vapour so he upped the voltage to 6 volts (it's amazing his heating coils last any length of time though).
Actually I thought my toothbrush was 3 volt but it is 3.6 ....unfortunately only 600 mah so it wouldn't hold it's power for long.
600 mah thats still about 3 times as much as the standard capacity of ecig battery
=180 mah so will last you much better.