While not recommended, double layer capacitors can withstand short circuits. By contrast some types of batteries may burst open or explode. Double layer capacitors don't contain heavy metals and highly toxic materials that require special disposal. This may minimize assembly errors and costs. Wide Operating Temperature Range .
Rechargeable batteries contain heavy metals and generally weigh more than double layer capacitors.
At larger sizes a rechargeable battery can weight more that twice the size of a comparable double layer capacitor. Principle of Operation . Briefly, just like other capacitors, a double layer capacitor stores energy in an electric field generated between two conductors and a dielectric. That is, a charge separation occurs at the interface between the solid and electrolyte. Two charge layers are formed, namely, an excess of electrons on one side and an excess of positive ions on the other side.