I have charged my MX 500 dirt rocket for 24 hours and the charger still is red. I took it off the charger and the back wheel went, but not going fast enough to stay up with both my feet off. When I hold the bike up, the back wheel goes very fast, but stops when I put it down.

The battery is probably bad. If a battery is fully discharged it can damage one of the cells in the battery. If you can replace the bad cell then it should charge correctly. Many of these batteries are made to be hard to open up and are hard to repair when they are opened. My best solution is to replace the battery and if that doesn't help then the charger is bad. When the charger is replaced then if both batteries are good then you will have a spare. I hope this helps.