I have a Brookstone U control Cloud Force helicopter and it won't stay charged for long. I've had it for a year and it used to be fine. A year ago I'd charge it for 15 minutes and use it for 10-15 minutes. But now I charge it for 15 and use it for about 45 seconds - 2 minutes. Is there any way I can change the battery? Or do something to make it last longer?