To diagnose a problem with the port, try using a different battery and cord for a while. Damaged Power Cord. The power cord is a wire inside a plastic sheath, and the wire can break with or without damage to the sheath. If the power goes on and off as the cord is moved or bent, the wire is likely broken.
You can work out if you're sore. Don't exercise the same muscle groups that are hurting. Do legs one day and exercise your upper body the next. By doing so, you'll still be able to get exercise and allow your lower body to recover and rebuild.
Although you should always consult your doctor before exercising with sore knees, there are leg exercises you can do that will strengthen your legs without hurting your knees. You might even find that building leg strength helps lessen your knee pain because the joints are better supported and stabilized.