I assume you mean the black rod (and not the discontinued blue rod). I too was underwhelmed with the black rod running on a single AW IMR battery. I wrote about my experience
here. The black rod (by design) supplies half the power of the white rod and this just doesn't work very well for stable waxes IMO. It's a shame too because I was hoping to use the black rod in a super stealth configuration. I'm pretty sure it would work much better with less viscous extracts like CO2 oils or ejuice although I haven't tried those with a black heating rod.
Since a lot of people will be getting a Core VV power supply very soon, if you want to try the power level of the black rod with a white rod setup set the voltage to 5.1v to 5.7v on the Core (or Iris) and see if that works for you. In my experiments with the white rod on an Iris the optimum voltage level for me using CO2 oil was around 6v and the optimum for very stable waxes and shatters was about 7v. More stable, hard to melt, extracts need more power to keep the oil/vapor engine running in the Herc. You can throttle the power by feathering the power button, of course, the VV supply just makes it easier to control and lees likely to burn your extract.
Hedo