[FMZPLAYER1]

The radio receiver slowly uses up the charge in the car's batt, that's what mine does. A 45 second quick charge will run the car for about 5 mins, (if used right away) or if left for an hour or two, that little bit of charge gets used up by the car's radio receiver (which is *always* on)
My car is a bit-clone, an "Atomic Z-car" actually, but the same should be true for just about any other car too.

If you have a digital meter, you can measure the battery (even when the car appears totally discharged)--there should be 0.3V to 0.8V remaining. When I first got my car, it had 0.3V in the batt a good sign, means the batt should be ok, if they go down to 0.00V, that can mean the batt is going bad (internal short may be developing)

If you see random voltage readings , that is normal too, when the batt has only about 0.8v left, the receiver goes into several startup/shutdown cycles. The receiver cuts out, then the batt voltage rises up under no load, untill it is just high enough to trigger the receiver to start working, which drops the voltage again..... It behaves just like a relaxation oscillator.