$9 at a slow charge
$9 at a slow charge speed/rate. Raise that speed/rate and your costs will go up. Power delivery is measured by utilities in amps, not volts. Speed up the charge rate, you raise the amps to accomplish it. Even at your rate, though, $9 at 30 days is $270, which is actually a lot more than our monthly power bill (which runs about $60-85).