@ymaes2020 sounds like a battery issue. Fully charged means that you can see it has the required voltage but you do not know how the battery does under a load. The only way to be sure that your battery is working to specs is by doing a load tech which means you will need special tools and software etc. I suggest you start off with a new battery. If nothing else you can use that as a known-well starting point should any further troubleshooting be needed.