Both peak voltages are too low based on my experience with Duralights. I had EXACTLY the same problem happen to me last fall in one of my packs in my KingCat. It would read 7.9 volts but would drop way down once a load was applied. Went to charge it after the weekend and it would not turn on the charge light. I phoned Jack at Duralight and a replacement was sent out. I caught the bad pack on my PowerBox. Good thing I had two batteries or I woud have LOST my KingCat!

Phone Duralight!
Dean W.
www.pstn.com