The battery on my key fob for 2013 model S85 only lasts about 6-8 weeks before I start having trouble with doors not responding to press on the handle or even having trouble when I click the fob. I have tested new batteries in both fobs (3.3 volts when I put them in) but they just don't last. Fobs are new as they were replaced by Tesla a year ago when they found a problem with the antenna and replaced it). Even the battery in the new Tesla fob (supplied by Tesla) only lasted 8 weeks. When I was still having problems, they tested again and couldn't find any further issues. When batteries no longer work they still read about 3 volts. I am out of ideas. Is this normal? Several times I have had to find the spot on the windshield to put the fob when battery wouldn't function and I was out of cell range. Solutions?