Haven’t found the exact device needed, so built my own.
This uses a simple two wire connection to any battery from about 24v to 100v.
Two set points:
Charger on-led on
Charger off-led off
set to 80v and 72v
When battery reaches 80v ac power is cut to charger
If battery self discharges to 72v charger will again be “plugged in”
I’m sure these are, or soon will be, available commercially, but for now I only find 12vdc or 220vac powered voltage relays. This is self powered by main battery voltage.