I had an issue with the low battery warning coming on and it only happened once but once was enough. I have 2011 xk vert, very low mileage. I have read on this forum about issues with low battery and using a battery tender. My thinking is WHY does one have to use a tender in the first place. What is the cause forget the remedy for a second. I had an electrical warning issue back in Oct 2013 not a low battery warning either. Anyway Jag dealer keeps vehicle for couple days says everything checked out fine but they did install a new battery. So now its Feb 2014 and low battery warning. Vehicle had sat for two days and on third day I got the warning. Drive the vehicle for road trip and everything fine no issues. But I email Jaguar usa and they contacted me and the dealer. I just let the vehicle sit locked for 3 days and no warning and started right up plenty of power. The Jaguar rep called today and they said since the vehicle sat 3 days no warning that I should wait to see if it happens again and then take it directly to dealer as they are on notice to take it right in. I am told verts have smaller batteries than coupes. They have 2 computer systems and do use power. Always keep doors locked and key fob away from vehicle when not in use. Jag says there is no reason for the battery to drain over a period of time. IF I was going to leave vehicle locked up for long period,months, a tender would be useful. The dealer service rep agrees also with the above. So we shall see what happens. I will let this forum know if a problem comes up. I do not know if this information is any help but this is what Jaguar says.