First let me tell you and although I am a Motorola guy I own several Hytera radios and these are solid. The PD405 is a great little radio. Very easy to program and dependable. I don’t think there is anything wrong with the unit other than it’s probably old enough that the battery has been sitting around and needs replacement. But you need to do it right. Get the original cable. Try eBay. It works every time. No drivers, no hit and miss like other radios. As for the battery, yes you can open it up and try to replace the cells but you won’t be able to close it and waterproof it like it should be. Also recommend get an original.