I have read a number of posts relating to the Start/Stop function and an associated mystery (because I can find no mention of it in the manual) auxiliary battery. Yesterday, while attending to some routine tasks, I opened the hood for a good look following the advice that it is located on the RH (passenger) side just forward of the firewall. If there is a battery there on my 2015.5 V60, it is very small indeed. I saw no sign of the (occasionally) pictured item. The only mention of "battery" and Start/Stop function together in the manual is the note that if this function is fitted, a replacement battery must be rated at 800 CCA, not the 680CCA spec for cars not so equipped. ???

On another note - the generic owners manual is marginally useless, being 75% devoted to defensive (i.e. anti law suit) warnings about doing unimaginably stupid things. Reference is made to an "on-line" manual available in the infotainment (I really dislike that word) system. This latter would, of course, be of little use if one were trying to deal with a problem in a non-starting car with a flat battery.

 

It's under the cowl cover at the base of the windshield.