I had a Gear 1 and never had a problem with that, its only started recently and I've only had the Gear 2 for about 6 weeks.
Could be the heat making me sweat and thats causing the rash with the battery terminals. Or it might be me just not noticing it till now as I'm always wearing it.
Would making the back thicker fix it? I'm thinking of a few layers of tape so the battery terminals are not actually touching the skin. That shouldn't get in the way of the charger but keep it off the skin. Another idea is to just cover the terminals with sticky tape and take it off while charging. Annoying but if it'll stop the rash it might be the way to go.