Thanks for your letter and interest in our products, we are pleased to reply:
1. What is the battery capacity and how it short?
Battery is about 550mAH and it can be used for about 2hours after being chargered fully
2. There is a charge indicator? How do I know that the battery is already charged?
There is a screen on the item, which will tell you the status, usually it should be chargered for about 2-3hours
3. You can charge the battery in off mode?
Yes, it can be charger both at on/off mode
4. Can the device operate from the current ( 5 volts)
5V, 1000mA, but there is no power adapter included in
5. If you hold the button fast track could be moved around the track?
Sorry as we cannot understand this very clearly
In addition, the item is good for use, and we have received our customers' praise, so you can buy and use it without anxious.
If there is anything we can do to help, we shall be more than pleased to do so, your order soon would be greatly appreciated