Ah! Went out to test again. Both running at 13.4 volts with engine running. I decided to push the jump button on the isolator to connect both batteries and they both shot up to over 15 volts. Wonder if I have a bad isolator?
I believe that's by design incase you drain both batteries. the solenoid will reserve a minimum in both batteries so when you use the jump button you have enough load to start up.
