A lot of the time on the Mino HD, it’s usually a tired battery due to the age of these. The issue with these is a dead battery will render it completely unusable. Tese days, most people opt to put it up for parts and see if they can at least sell it to get a few bucks out of them.
While Cisco no longer supports them, you can buy a 3rd party battery. However, it’s not always the best option with the age of these camcorders compared to the advancements in even a 3-4 year old smartphone, and standalone camcorders. If you insist on a standalone camcorder you’re usually better off buying a camcorder or point and shoot with AVCHD and MP4 options in many cases. That said, the smartphone in your pocket often is good enough for many as well so get a tripod mount for your phone and try to shoot with that if you have a lot of space (128GB minimum, 256GB+ recommended).