Did you call DP customer service? This is a great forum to get other players input on fixing/repairing your own marker. But when you have such a great customer service in DP, why not just call them and they will help correct the problem.
Know that I said that here is a few ideas:
I know you said you changed your battery, but just make sure the battery is a good battery.
We already changed batteries to find out the battery wasn't any better then the original. (damn WALMART batteries)
Good Luck, with the F8. Give the boys at DP a call.
Service and Parts - 10am to 6pm PST
(909) 869-8801 | firstname.lastname@example.org