I have a 2007 BMW 328xi with keyless access, and have been having some difficulty with my key fob, as of late. I did not use my car for about a month while I was away during February, and now it seems that my fob remote works only sporadically. I can't lock or unlock the doors with the remote access buttons, and will have to resort to taking the little key out of the fob itself to manually unlock the front door. Sometimes, after leaving the key in the ignition, it will work, but only temporarily. Is there anything I should be doing, or a battery that I can replace, that will help to preserve the life of my key, or does it sound like it's on it's last leg? Thanks.