How long can the capacitors in small electronic equipment hold a charge after the equipment is turned off? Like small Radios, mp3 players, phones for example. After you turn off a radio, how long will the capacitor hold energy?

Replying to [cuihua]:
A really good capacitors with nothing to drain off the energy can hold the voltage for a couple of days, maybe weeks, but most capacitors used in radios might hold their charge for a couple of hours if nothing is draining them.

Replying to [cuihua]:depends on the size

Replying to [cuihua]:Generally, the answer is in milliseconds. But in the case of flash memory, as used in MP3 players, the unsulated (floating) gate transistors can maintain their charge (thus their memory) for years.

Replying to [cuihua]:That really depends on the impedance of the circuit around it, and its leakage rating.

Charging or discharging a capacitor may cause energy loss even if no dissipative elements are apparent.

Quoting from [yufang]:


Replying to [cuihua]:That really depends on the impedance of the circuit around it, and its leakage rating.                                                                                                                                                           

I agree with this. And plus, it depend on which capacitor you are talking about, I mean, the location of the capacitor. Any other precise answer would be very much welcome.