Hello, about a year ago I bought one of your oscilloscopes (the handheld 2D72) and it’s been working perfectly up until about a week ago where it stopped working on battery power. I checked the batteries and they are at 4.1v and I tried replacing them with brand new batteries also at 4.1v and still nothing. It will work fine when powered by usb. Is there a way I can fix this or get it serviced?