"you'd better have the car in a heated garage (it doesn't charge well when it's below -15 C / 5 F)." This I find interesting. Why doesn't the internal resista

"you'd better have the car in a heated garage (it doesn't charge well when it's below -15 C / 5 F)." This I find interesting. Why doesn't the internal resistance of the battery raise the temperature sufficient that this doesn't matter? If there's some reason it couldn't, then why not add a few temperature-modulated resistive heaters?