2009 Grand Caravan Electrical Problem

Any ideas on what we found this morning?

Went to start the van and  there was no power at all. No interior lights, no
response to turning the key, etc., real dead battry stuff.  I hooked up a battery
charger and when I turned it on all exterior (and I think all interior) lights went
on (headlights, tail lights, turning light) even though the car was off and the
headlight switch was in the off position.

Turning the charger to boost, the lights went on again and then went out after 5-
8 seconds.  After that the van started perfectly and is running perfect.

Any ideas?  Thanks.