Just take extra precaution while performing it. I would put it on a mid-low setting, because those heat guns are pretty strong. If you want to be super cautious, which should be the case because it's a battery, keep untreated sand available in the event something happens during the process (pops, vents, etc).
As for where to apply heat, where the remaining adhesive is. The adhesive is elastic, so on the area where you have it removed use a playing card, or something similar, to feel out where the remaining pieces are.
hope this helps.