I pay all my bills electronically - everything - rent, utilities, car insurance, cellphone, CC; some are auto payments and some with variable amounts, I pay by logging into their secure website.
I either pay it by providing my debit card number or my bank routing and account numbers and I’ve never encountered a fee for doing so.
The only time I had to pay a fee was when I was between jobs and had to pay my rent using a CC (not my bank debit card) and had to pay a 2% fee.
Evidently some utilities charge a fee for online payments and some don’t.