I've had my FT 991 for some years now but only recently started using it in earnest. I have noticed that the VDD meter which I am assuming is a battery meter, does not display the state of the battery. The display sits at 13.8 volts even when the battery drops. Is there a DC DC converter that holds VDD at 13.8 volts? That makes no sense to me but I cannot think of any other reason why VDD is staying on 13.8V.