Quote Originally Posted by 87SunSportMikeyD View Post
The SurePower is both a battery seperator and combiner. The system keeps the batteries seperate for everything except starting-assist IF the main battery is low. Your stereo would be hooked up to your 2nd battery. So if you drain your stereo, it is dead (hypothetically). Then you would start your boat and the SurePower would link batteries and begin charging both. Since the batteries are now linked you would get stereo power back as long as you were driving and charging.
So it links the dead battery and the charged battery together, thus dragging down the charged battery. Would that not be correct?

What I've done in the past with situations like that, is to use a 200A Relay/Isolator. If does basically the same thing, but instead of using the ignition key to trigger it to connect, I wire in a manual toggle switch. That way the boat owner can leave it separated until the boat is started and idling, then flip the switch and connect the batteries. That's only if they don't have an onboard charger because it's pointless at the end of the day to connect the stereo battery to the alternator for a 10 minute ride back to the ramp.