why are chargers called chargers?

charge, n, adopted from OF-F, comes from OF-MF chargier, to load, whence "to charge", orig to load, hence to place, upon someone, a load other than of weight... A charger, whether a large platter or a cavalry or ceremonial horse, carries a weight ...
.......-- Origins A Short Etymological Dictionary of Modern English

Chargers are also called service plates or place plates. They can be made of china, metal or wood. A charger is in place when the diners come to the table; the napkin may be centered on it, with a place card centered on that, in which case the diner and not the server removes the napkin for use and puts the place card aside. A soup plate, with or without an underliner, is placed on the charger; a soup cup requires an underliner even if a charger is used. A plate of oysters or clams may also be placed on the charger.

The charger is removed after the soup and shellfish courses, so that a plate for the fish or meat course may be substituted. For proper removal, the server must stand behind the diner and lean to the right to remove the charger and then immediately lean to the left to slip in a fresh plate, so that at no time during a proper dinner, until just before dessert service, is the place in front of the diner empty. A dinner plate may be used instead of a charger, and is just left in place for use during the main course.

My chargers are metal.