Herself's car keyfobs started going flat, and the car rightly complained in time. I managed to replace the lithium cells* in each keyfob easily enough. Only at that point did I RTFM, and found the door keyholes cunningly hidden under pry-off covers in case of emergency.

* Side peeve: If there's only one, it's a cell; if there's a stack of them sold as a unit, they jointly are a battery.