I hope this helps someone as it did for me. First I'd like to thank the member [sorry, I can't find his post to give him some much deserved recognition] who suggested blowing the fob out with compressed air. I'd been away in France for a couple of months so my car was laid up [with a trickle charger connected]. My keys had been in a drawer in the unheated house for months so they didn't have the luxury of residing in my pocket or in a warm car etc. for a long time. I tried to open the car to move it and I had no response from either key fob. The light on the fob flashed rapidly at first then nothing. New batteries at 3.25 V in each still gave me no fob light. I'd tried all suggestions in the various forums, all to no avail. I even salvaged a battery from a disgarded Vape, charged that and paralled that with the new fob battery just to see if it was a battery current draw issue. Then I remembered what I had read about the compressed air. Fortunately, as I have 2 cars and 4 motorbikes (don't ask), I have a compressor in the garage. "Nothing to lose" I thought. .... RESULT!!!!!. So I blew out the second fob with just my new battery in, [no vape backup]. AGAIN, sucess.
So thanks again to the guy that posted about the benefit of a blow job. Also my low key battery warning has gone ... WHOOP WHOOP!! The keys now reside on hooks attached to the front of my boiler.