I would suggest eventually investing in some higher quality battery packs (up to 3000maH is optimal) and the acquisition of a peak battery charger.

This is because the charger that comes with the HL tanks is a very simple device that applies constant current to the battery pack. There is no charge termination method used by the charger. During the recharging process, once batteries reach their 100% charge, the cell starts to heat and the internal pressure builds up, causing the battery to eventually rupture or vent electrolyte.

I think, however, that you should initially charge your 7.2V pack with the included charger for about 12-14 hours if I'm not mistaken.

-Harq

EDIT: Agreed on the smoke generator's performance increasing with a better (or fully charged) battery. Mine has been churning out the smoke at a increased rate. I had seldom turned it on when I had a fresh battery but had waited until it was depleted 50% or more to try out the smoker.