How long before a capacitor looses its voltage?

 

How good is your capacitor?

A good quality Teflon capacitor can hold a charge longer than you would care to wait. An old aluminum electrolytic might loose half its charge in an hour or less. These are free-floating capacitors with no electrical connections.

 

The dielectric has leakage properties, best to study that (math) in vacuum conditions.

In air (humidity), electrons will leak across/out the terminals via air.

But surely, a poorly made teflon can leak faster than an ok made electrolytic.

 

But surely, a poorly made teflon can leak faster than an ok made electrolytic.

Sure, if someone goes out of their way to make it really, really, really poor.

Electrolytics typically have leakage resistances in the 100 kΩ to 10 MΩ range.

Teflon and similar capacitors typically have leakage resistances in the 100 GΩ to 10 TΩ range (i.e., six orders of magnitude larger).

 

How long before a capacitor looses its voltage?

.
How much do You want to pay for this Capacitor ???
.
.
.

 

This is a trick question!! It depends very much on what is connected to that capacitor. In addition, it depends on what sort of capacitor, and what the ratings for that device are.
So that question is like asking "How fast can a car go?"
Mostly, capacitors not connected to anything do not become charged, and even wired into a circuit, it is variable.