Well, today I checked the batteries and they both read about 12.05v, which is good, but doesn’t say how much juice is in them.
So, next I went ahead and plugged up the block heater and let it warm up for a while. I did some other stuff and came back an hour later to try to start it, and it turned over right away. Yay! Thanks for the suggestions.
I let it warm up a few minutes and then drove around the pasture for a spell. After ten minutes or so, I parked it back in the barn.
After I turned it off and jumped off, I took a look at the big back right tire, and thought it looked a bit low. Not flat, but seemed kinda low to the ground. I figured it may look like that because the barn floor is sloped downhill, and maybe the weight is shifting over onto that tire.
I cranked it back up and took it back out to check both tires. It seems that both of them get a bit “squished” when they roll, and more so on the downhill tire when driving across a hill. But, the right tire does seem to roll a bit lower to the ground than the left.
I believe the tires are filled with fluid (calcium chloride). Is it possible some has leaked out, I didn’t see any obvious damage to the tire? Or, do tires with fluid in them act this way in cold weather? These look like almost new tires with hardly any wear on them.