What's the eutectic point (lowest freezing point) of salty battery acid? Shouldn't we see that flowing on the surface, almost no matter what the abient temperature?

But we don't see current flows -- apart from whatever substances and processes are forming the gullies on cratersides.

Something is limiting fluid flows on the surface at present. It could be the chemical composition of whatever fluids may make it to the surface, it may be temperature, may be atmospheric pressure, or a combination or -- who knows -- it maybe something else that hasn't been thought of yet.

The idea that liquid water can exist at the surface should long ago have been accepted. Of course it can (at least for a while). There is also an apparent abundance of water ice near the surface in equatorial latitudes -- ice which ought to be subject to some form of melt from time to time. The discussion point by now should have moved on to the question of why it doesn't do so more often. Why are fluid flows relatively rare, though not completely absent? How were conditions different enough in the past to permit extensive flows?

And ultimately we have to ponder what substance flows now, and what flowed in the past? In other words, have there ever been extensive liquid water flows on Mars, or were the riverbeds and canyons long thought to be carved by flowing water actually the result of -- say -- battery acid flows?

It's a different world, after all.