I don't know where you will be in France, but I would use Plugshare to see where you can find chargers. Plugshare is crowded sourced info.
Standard chargers are J1772. CCS will be for level 3 / quick charging. Nissan uses CHADeMO for quick charging. Tesla has their own proprietary plugs.
In the US, you can pay for charging at most stations via app or a credit card. Common brands for US public chargers include EVGO, Chargepoint, Electrify America, and Blink. Each has their own app where you can add a credit card. These apps will also display charger locations too.

If your rental is a Tesla, the company should provide a charge card. There is no way to access a Tesla Supercharger without owning a Tesla. National does not charge any fees for recharging on the Supercharger ("free electricity").

At least with National, you do not need to return the EV fully charged. I am not sure about other brands like Sixt, but I assume they would follow the same policy.