According to wikipedia, the name “Chargers” was picked by the original owner because he liked the rallying cry “charge!” at Southern Cal games.
But the lightning bolt logo makes you think of an electric charge.
I saw a cover from a 1963 program of a Pats-Charger game in Boston, and it had a picture of a bunch of horses to represent the Chargers, as in “charger” being a knight’s horse.
The Chargers have always had the lightning bolt;ergo, they’re called the Bolts. I guess in their early days that name had not been firmly attached.