Non Mopar Battery Isolator question

There used to be two quality options in Voltage Sensing Relays. Unfortunately Blue Seas bought BEP Marine and has gone all Mallory on them. Can't get the product from previous vendors, marine outlets are now the only place that I can find these things.

Premise is that right after a start that the starting battery should get fully re-charged as a priority. then the Aux battery bank can be brought up to full charge. The relay monitors the voltage on one or both of it's terminals. When the one or either reaches a full state of charge voltage the relay closes and connects the other battery to the charging source. I see these as one step better than a constant duty solenoid because there is a little management of charge happening rather than just working the alternator to death.

http://www.westmarine.com/buy/blue-sea-systems--mini-automatic-charging-relay--14152557