terry writes:

Make that say one tenth of a cent; in other words it will cost around
2 to 2.5 cents per 24 hour day that it is plugged in and not charging.
Hardly worth bothering about?

For anyone connected to the North American power grid. On the other
hand, it might be worth unplugging for off-grid people who generate
their electricity by solar panels or windmill and store it in batteries,
since their per-kwh cost is likely to be many times higher.

Dave