Must be the Brit Air or...
I got 6 1/2 years out of my oem batt., and I only changed it
out so I could do it on my time, not "its time".
Short trips? Something draining it?
I'd cop a Battery Tender or something equiv. in the UK
and give it a good, slow charge on occasion.
GL,mD
http://batterytender.com/deltran_europe.php