2012 X5's were built from ~June 2011, so it may be older than you think. I've gotten 6 yrs, 9mo and 7 yr, 3 mo from my E70 & E60 original batteries. Never left me stranded, but got tired of the battery discharge warning. If indeed you still have the original battery, there's a date code on the top of one of the battery posts. It shows
wk no., and year mfd. If short trips are the problem you can get a little more out of it if you put a 10A AGM charger on it overnight. Schumacher chargers are ~$50 at Walmart.