My battery problems were caused by Bad batteries in the cars, I have replaced them and its fine now. As for the speed difference, I have noticed differences in the cars when used with the regular controllers, But when they are ran with the special (on the same settings) there was no difference. HOWEVER, I have noticed that MY Skyline sucks and so does my Beetle. But my other 4 cars are fine. There are many "problems" that happen with the older cars when they come in contact with pet hair or dust, But the new DigiQ-Rs have sealed gear boxes to stop this. I recommend that you spend the extra cash and upgrade to the R.