You need a split charge relay...Stinger SRG32 is the best one. There are also cheaper 180a relays available.

The relay will isolate the batteries when the car is off and link them when the car is started.

As for dedicated ICE batteries, you want something like Yellow top or Shruken (entry level), followed by Kinetik, Oddyssey (mid level), followed by XS Power (top end)