I had the same problem, the x3 sat in the cold for a couple of weeks, wouldn't start. I'm going to have the dealer check the battery next time I come in for a service. The solar charger sounds interesting, but is pricey. And it'll be no good if you get snow on the windshield which blocks out the sun. The $30 battery/starter unit is the way to go in my opinion as long as it works as advertised.