40 A solar controller

I had been using a 60 amp Bobbier Sun Selector until it failed a few weeks ago after 25 years. They're no longer in business so I replaced it with a Sun Yoba 80 amp MPPT controller from eBay for about $80. Works well so far. Has an LCD screen with PV volts/amps, battery volts/amps, and other stuff.

IMHO, the big name brand units are good and worth the price premium. I am using Morningstar (TS-MMPT-45) and am very happy.

Given your question, it sounds like you may be interested in either an actual battery bank monitor (not just voltage, which tells you nothing). For this, the Bogart Trimetric RV-2030 is very good. Or, maybe, just the solar panel output information in which case a remote panel for your charge controller (it is the TS-RM-2 for the Morningstar MPPT controllers).

If I was buying an mppt I would go with Morningstar. I have 12 volt panels so I have Bogart SC2030 pwm along with the trimetric.

Go with the Morningstar

Blue Sky Solar Boost 3000i 30 amp MPPT Controller

Solar Boost 3000i

Thanks everyone for your help. It is amazing how just a few suggestions can push you where you were stumbling towards.
Many thanks again.