I have a Heart Interface Link 2000 monitor that I recently learned is reporting battery voltage that's about a half volt below what I measure at the battery. Other than that the displayed voltage behaves as you would expect - high when charging, gradually getting lower when not charging. The problem is not my handheld voltmeter. There's also an analog meter on the switch panel that agrees with my voltmeter. I can't imagine what could cause this discrepancy. Any ideas?