Those LED light just indicate the voltage. When the engine is running they will always indicate full as alternator voltage is about 14V. If you battery voltage drops that fast to indicate "empty" when you apply a load with engine off the battery are likely bad as rvsprinterguy mentioned.
2013 Airstream Interstate Lounge EXT on 2012 Sprinter 3500 170Ext
Formerly: 1973 Dodge B300 DIY pop-top conversion