Funnily enough, I had to call the AA out to my daughters 2015 Ford Focus for the same reason. She only uses it once every few weeks now and it has the original battery. The car has stop start technology (although never used) and, as a result, a replacement battery would be £264. Ouch. On my other daughters previous Focus (without stop start technology) the new battery was just £120. The chap said that the original battery is still OK if used regularly and if we bought a new one we would have the same problem in 6 months time. Of course, it’s all progress ?