[Motorin Mark]

Hey guys, so I do not use my M3 (2008) as my daily driver. I drive it every two or three weeks on the weekends. The last two times it has sat for two weeks the clock and the trip meter have somehow reset to 0 and both have to be reset. Does not seem to matter if I hook up my battery tender or not. Is this a sign that my battery is going out? or just some type of pre caution that the car makes on its own? Help please.

Thanks.