Miss Manners: Should I have asked permission to plug in my electric car at party hosts’ charging port?

DEAR MISS MANNERS: I visited a family for their child’s birthday party. It was my first time at their home, and I wanted to remain polite.
I drive an electric car and to my delight, their home had two charging ports prominently visible and unoccupied. Would I have offended if I had plugged my vehicle in? Asking permission from an already-busy hostess seemed intrusive.
I know that in a reverse situation, I would have been more than happy to have someone charge at my home. A four-hour charge, even at high electricity prices, would work out to around $10 — a cost I would be happy to roll into the usual party expenses. May I help myself?
GENTLE READER: That the charging station was prominently visible makes it a convenience for the homeowner and a temptation for you — not an invitation. The cost is beside the point.
The polite thing to do when visiting another’s home — for the first time, or the 50th — is to ask permission. Miss Manners is confident you can find a quiet moment to do so, if a top-off is necessary.
(Please send your questions to Miss Manners at her website, www.missmanners.com; to her email, [email protected]; or through postal mail to Miss Manners, Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106.)