I just bought a second hand hoelshot. I first set the time and after a few days noticed it was off by several minutes. I had the chronograph hand moving in time with my second hand and thought maybe the added stress on the system caused the time function t9 lose time. I then turned the chronograph off and reset the time. After 3 days I checked it again and I was 7 mins slow. The second haND seems to be running fine without any indication that the battery is bad. Do you think it's a battery issue or a service issue?