Wiring an outboard Kicker to my 1986 Seville Cuddy I/O

[kmesr9]

I searched and didn't see this so my question is: I recently purchased a kicker motor that has electric start and is capable of charging my batteries on board my 1986 Seville with a Merc 140 I/O and I want to wire it into my 2 battery system. Is there a proper way to do it using my current setup which is a 2 battery switch or do I need to purchase a battery isolator for a 2 alt. 2 battery setup or? Thank you for all of your help!