Simplest battery monitor and shunt? Advice for non-expert

While as an installer, I love the idea of the Victron Smart Shunt, it concerns me that it needs a smartphone. Many of my clients shut off the phone and pack it in a Pelican box on departure. These devices are not know to love sea water.

I don't have one because I really like the old Bogart Trimetric staring me in the face and being hard to ignore. If I have to fire up an app to know the status of the house bank, that is just too inconvenient for me as I have enough to do already.

Matt