Suppose you have two capacitors and want to use them to store the maximum amount of energy by connecting them across a voltage source. you should connect them

Connect them in parallel

Explanation:

The energy stored by two capacitors connected to the same voltage source is given by

where

is the total capacitance of the two capacitors

V is the voltage of the source

In order to maximize the energy stored U, we need to maximize . We have:

- In parallel, the total capacitance is given by the sum of the individual capacitances:

- In series, the total capacitance is given by:

Comparing the two equations, we notice that , so the parallel configuration is the one that maximizes the energy stored.