I had a backfire when I last used my Husqvarna riding mower, as I shut it off. I went to use it, again, about 12 days later, and it won't start - nothing at all happens, when I turn the key (with the blade in idle, the clutch pushed all the way in and the engine in choke). There is no sound, no readout in the small LED window, beneath the steering wheel. Is that usually just a battery or something more?