I don’t know why you were downvoted, because this is true. I have my battery in the RTT with me so it stays at operating temp. Here’s the one I have. I put it over me, and then I put a large sleeping bag, zipped open, over that. That way, I can have the battery bank under the bag, too. (I also have a mummy bag and other blankets I can use or remove as needed, and in a real pinch I can use the down mummy bag inside the XL bag zipped up.)

I don’t run the electric blanket all night. It is very slow to heat up but does eventually provide a lot of warmth. I turn it back on for a while during the night as needed.

Also, don’t forget to put the next day’s clothes — base layer, at least — under the covers with you. Much better than putting on frigid clothing in the morning.