I agree. Forget about weight. Go with an AGM battery. These cars are known for draining batteries if left to sit too long like any modern car these days. The XF was just before its time on parasitic battery drain so it shocks some people. I went with a Diehard Platinum AGM. Not cheap but also no worries about letting it sit for a while and having a no-start situation. I also have a rapid disconnect on the battery so if it is going to sit for more than a week I can easily disconnect it with a few quick twists. I haven't pushed this battery to the breaking point so I've no idea how long it could last hooked up without being driven but I don't want to do that. Drain a battery that far and it never comes back to full storage capacity... do it a few times and the battery is junk in these cars.