When a capacitor is charged it stores the energy. What happens to the charge after removing the charger?

Question

What happens to the charge in a fully charged capacitor when left alone after charging? I heard it discharges, but to where?

Answer 1

Any capaictor has leakage current, that is, unintended current due to surface contamination or bulk defects in the material, or just the fixed resistivity of the dielectric material.

This leakage can be modeled as a high value resistor in parallel with the capacitor.

And it is this leakage current that causes any capacitor to discharge over time.

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Answer 2

Just as a battery left alone will go flat so does a capacitor, the charge will just leak into the atmosphere but I think that they have designed one now that stays charged for a very long time, a couple of months or more. They are talking about being able to use them instead of batteries now the advantage being that you will be able to charge things like your phone etc up in seconds instead of hours/minutes.

MIT researchers are developing a battery based on capacitors that utilize nanotubes for high surface area, enabling near instantaneous charging and no degradation. Estimating ~5 years to commercialization.

How it Works

Rechargable and disposable batteries use a chemical reaction to produce energy. The problem is that after many charges and discharges the battery loses capacity to the point where the user has to discard it.

However, capacitors contain energy as an electric field of charged particles created by two metal electrodes. Capacitors charge faster and last longer than normal batteries.

The problem is that storage capacity is proportional to the surface area of the battery's electrodes, so even today's most powerful capacitors hold 25 times less energy than similarly sized standard chemical batteries.

MIT researchers have solved this by covering the electrodes with millions of nanotubes, which are essentially tiny filaments. The nanotube filaments increase the surface area of the electrodes and allow the capacitor to store more energy.

The MIT capacitor thus combines the strength of today's batteries with the longevity and speed of capacitors

This technology has broad practical possibilities, affecting any device that requires a battery.

Small devices such as hearing aids that could be more quickly recharged where the batteries wouldn't wear out.

In automobiles you could regeneratively re-use the energy of motion and therefore improve the energy efficiency and fuel economy.

hybrid cars would be a particularly popular application for these batteries, both for the speed of recharge, capacity for charge, and because current hybrid batteries are expensive to replace