Why does my 2013 Dodge Dart battery keep dying?

I’ve had my 2013 Dodge Dart for a year and a
half and for the past 3 months it keeps dying.
Every couple of weeks the battery just dies
and the car won’t start. Yesterday it did it
again, this time there’s now a buzzing sound
and the battery light comes on. I’ve taken it
to two different dodge dealerships one
charged to have the engine shampooed then
told they don’t know what’s causing the
problem, what a waste of money. When we
took it to the second dealer they just said
they didn’t know the cause then tried to soak
me for a bunch of other things like wipers,
tires and breaks when all those things are
fine. When it died yesterday I had it boosted
it made it half a km down the street then died
again did this all the way home. I charged the
battery up and the car runs the buzzing
sound is still there but I’m too scared to drive
it in case it dies again. I find it highly
unprofessional and pathetic that two DODGE
dealerships can’t even figure out what’s
wrong with THEIR car. I’m beginning to think
the alternator is not charging the battery back
up or there’s a short that’s causing the
battery to keep dying but have no idea what
short it is.