You can go fishing when it is below 32 you just have to fish until it warms up outsideI dont use my boat for ice fishing. If its below 32F in my garage (unheated) for long enough to drop my batteries to 32F then its pretty dang cold out and not likely I am going to get the boat in the water the next morning anyways. I can check my battery temperature right now from my office using the bluetooth in the Ionics. Its 26F outside and my batteries are at 38.4F. I can think of one place I could fish tomorrow but I wouldn't be going until it got above freezing, so if I had to charge my batteries I would have done so 6 hours ago and they would be charged already... but if need be I would just go put an old school work light with 100W bulb in the box during morning coffee and those batteries would be above 32 in no time, give them a couple hours to charge up and then hit the water when its warm.
The lithium batteries charge stupid fast, plug in when done fishing and unplug before the temp starts to drop. Plug back in when batteries are over 32F, even if I forget its no worry.. they have low temp protection so they won't allow me to charge them when below 33F.
You can draw current (use them) down to -4F. That would be a fun challenge to find a place to fish with the boat when its -4. I've been in some cold weather while walleye fishing the river, but -4 is going to start freezing over the mighty mississippi even.