My car lock often will not open the door. I believe the battery runs down when it sits overnight, although there is nothing to drain the battery. How can I determine what is causing the problem. I know it is not the battery, it's new. This was first a problem, after I had a new stereo put in about 3 years ago and it has continued. The car always starts, but the lock is a big problem.
You may have a small amperage drain on the battery that is just enough to keep the door locks from working. The other possibility is the battery in the key fob may be starting to go bad and needs to be replaced.