Use your lightning bolt (which does not cost energy) to charge light post, battery, or another object that can be drained of energy. Drain it after it is charged. If the object does not explode, your entire energy meter will be filled.

Shock a pedestrian, then walk up to them. Lock on, then repeatedly press Square repeatedly to restore your power.

After killing a person, shock their body with your basic lightning bolts that require no energy. Press L2 while they are sparking to absorb the energy and recharge.