Battery died while in Neutral

So the 2011 Prius was sitting around for a month as my friend was out of town. It is parked in my side yard. The hybrid system started just fine, and I put it in neutral while I was sitting there about to drive it. The battery shut off while in Neutral. From what I've read, the battery won't charge while in Neutral. The car will not accept a jump from another car using jumper cables, but it IS GETTING POWER from the portable 10amp charger I set up. The lights in the cabin now come on, the doors respond to the key, etc. The engine will not start though, even though the battery charger says "fully charged". As soon as I unplug it, there is no power to the Prius. I think the problem is that there is no way to get it into "P", which according to the manual, is the only way to start the engine.

The hybrid system will not start in Neutral, according to the manual.

Does anyone know how to get it into "P" at this point? The light just doesn't come on when I hit the "P" button. I've tried simultaneously holding the Power button, trying to switch "mode" and everything. Nothing responds.

Also, the little engine light saying "CHECK" is on solid.

All of this ONLY while the battery charger is plugged in/connected to the vehicle.

Any help would be appreciated!

 

As soon as the battery charger is unplugged, there is no electrical on at all in the Prius, even the doors won't respond to the key, etc. when the battery charger is disconnected.