Question: how much power does a battery tender use?
Answer: 054 in a month and that is if you operate it 24/7. Maintenance charges can go up and down to 100mA so you can get a peak of $. 10 a month. So that is how much does it cost to run a battery tender and as you can see, it is so tiny that you probably have errant light bulbs that consume more power than the tender.