This is very little money.
If campground owner takes an issue with this, tell him that battery is 0.5 KWH.
Even in expensive California 1KWH costs 20 cents. If he's got enough brains to divide 20 cents by 2, he'll know that it costs him 10 cents. Camp electricity rates can be higher than residential, Ok - give him a quarter
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OTH, if the camp owner/manager can't divide 20 by 2, I suggest staying away from him and his camp because either his IQ is dangerously low, or he is looking for trouble (or both).
Charging it in a camp washroom you'll annoy other campers wanting to plug electric shaver in, or charge their phones. Bike battery looks big, they don't realize that it's only 0.5 KWH.
I think there are typos in the table by Arizona rider linked above. It's 11.86 CENTS, not $11.86, and this is per kWH, not per kW. Az is cheaper than Ca.