Yup. That's what it's supposed to do. Charging source above 13.4V = blue light on = batteries in parallel.
There are two different schools of thought when it comes to WHICH battery you are connecting your charger to:
- Some say put the trickle charger on the primary battery and let the isolator add the AUX battery in later, as this ensures you always have a full primary battery, especially if only charging for a short period of time.
- Others say to put the trickle charger on your AUX battery and let the primary battery get added in later, as the AUX battery is likely the one most in need of BEING charged and the primary is likely always full (if the isolator did it's job), as you're constantly using it for all your accessories when the bike is not running (e.g., playing your radio for hours while enjoying a barley pop or three, etc.).
Honestly, unless you're running your AUX battery down to near nothing and then ONLY putting the charger on for a very SHORT period of time, I don't think it matters which way you go, as both will eventually get charged (e.g., overnight).