Hey sean, A battery charger won't tell you anything about the overall state of the battery. When you see the 80-90% it is showing the amount of voltage in the batt. ie9.6-10.8v. It is the amperage that matters. A load tester will give you that reading. You can have a dead battery that will still show 12v. I would suggest you spend 50 bucks and get a gell battery. It will last 2-3 times as long as an acid type, and pay for itself. Your cdi works off 12v input, and if there is a short inside your batt. your stator cannot produce enough voltage to trigger spark. one way to confirm this is to put a socket in a cordless drill, and use that as an electric starter. you can run it on the flywheel nut. you will need a volt meter hooked up to the 12 positive at the battery. with the spark plug removed run the drill and note the voltage. If it at or below 10v the scoot cannot run. This would be my bet! You can then disconnect the battery, and see if the voltage comes up above 12v. should be 13.5-14.5. if you still have low voltage could be a bad stator, regulator, or a wiring problem. take it one step at a time and you will find it. Ps. Have you checked the main fuse on the battery?