Sphero should require approximately 3 hours to fully charge if his battery is depleted. It is important that he rests with his heavy side down in his charger or the process can take much longer. Once Sphero’s charging is complete, he can rest in his charger until the next time you roll with him. If you are not going to play with Sphero for a long time, leave him off the charger to rest and start charging him again when you'd like to play. While charging, Sphero may be warm (~100 degrees). This is considered normal.
If the blue light on Sphero’s charger does not turn solid (no flashing) within 3 hours, please make certain he is resting heavy side down in his charger.