If the batteries in your BMW remote have died, you will not be able to start the car or unlock the doors using the keyless feature.
Follow the instructions in this guide to learn how to manually start your BMW. This guide will assist you if the key fob batteries have died or the key fob is not working.
If the main BMW battery has died, follow this guide to get into the car, then follow the instructions on this guide to jump-start a BMW with a dead car battery.
If your BMW doesn't start, it means the key wasn’t recognized. A check control message may appear on the dashboard stating the key was not recognized. Your key may be defective or the ignition module has a problem.
Try the procedure one more time, making sure there is no more than two-second delay between steps.
Also, try the same procedure with a spare key.
For help with changing the key fob batteries follow this guide: How to change BMW key fob batteries.