I do not have a tiered electric rate so I have been charging when I get home and leaving the Prime plugged in overnight. Is there any harm done by leaving it plugged in like that or is there a reason that the charging cord should be disconnected as soon as the charge is complete?
I don't believe it will cause any harm. Probably more good then bad. My Prius Prime the heater is running to keep the battery warm. I don't have any schedule departure time or schedule programed into it. It's been charging two day with no worries. Posted via the PriusChat mobile app.
i think toyota says the 12v will drain if you leave it plugged in after it's done charging. plus, it's not good for li-on to stay full, especially in warm weather, you're better off using the timer, and setting a finish time for when you leave in the morning.
That is a little misleading, since it's not ever "full". 100% is indeed harder on batteries. Recharge of Prime only goes to 85%. For long-term storage you don't want to leave it at that 85%. But this topic is only about overnight. Leave it plugged in until you leave for work in the morning. And as suggested, set the timer for close to when you will be leaving. The rest period (known as a "cold soak") for the battery does promote longevity.
There are always drains on the 12v, so no big deal. For example, that's what powers the interface for the phone app, allowing you to remotely interface with the car. There is also the proximity detector for the door locks.
Actually, there is an entry in the manual about how to disable the locks to prevent drain from long-term storage. Put it this way, I have never heard any plug-in owner ever express concern over the 12v battery simply from leaving it plugged in short-term. Warnings are legal CYA that's par for the course. No need for concern.