https://www.amazon.com/gp/product/B0026TBFIO/

I have these in my unpowered garage at my cabin. Put one in a window on each side, so not even direct exposure. One on my riding mower, and one on my go kart. After sitting for a good 5+ months, both machines fired like the batteries were brand new. Last winter I had to jump the mower after sitting for the winter.