70 qt Coleman Xtreme & efficiencies

When mashing (read: batch sparging) 5-gallon batches in a large cooler such as this, would the unused space have any effect on efficencies outside of it just being a larger area to heat and its associated deadspace?

I don't think so, but I've wondered a few times about it. I know fly sparging is better with a thicker grain bed but shouldn't matter for batch.

I've got this exact cooler and I've done my last couple of 5 gallon batches in it. In all cases it has held the mash temp within 1-2 degrees for 60 minute and 90 minute mashes

I preheat the cooler while my strike water is heating and it retains the heat well.

I mash at 1.25qts/lb and have never had a problem.

Also, I use a copper manifold in the shape of a loop and I've been averaging over 85% efficiency on my last couple of batches.

I've been real happy with this cooler. I was worried about 5 gallon batches as well, but I haven't had a problem yet.

I have the 80qt and when I was making it I to was worried that it was going to be to big for 5 gallon batches. The way I fixed that was I just started brew 10 gallons and have not had any problems.

Have done a few 5 gallon and it works just fine.