wow no year stated, nor car. a willis jeep> 1945?
in 1945 it has no Alternator !
General answer , for all cars:
dead parked, or dead moving ?
no person can help lacking that critical fact,
to me like, impossible question !
if it goes dead moving the alternator /gen system is failing.
if the battery goes dead parked, that means you have phantom drain.
we can find out which it is , with a $10 DMM meter at walmart
$20 is a better buy.
so if it drains over night check for lamps stuck on.(aka. dark current)
if drain driving, then.
check for 13.3 to 15vdc, running, engine.
if low, the alternator system (charge) is failing
at no time did i say any part was bad or to buy them. (i never do until i do tests)
works on all cars.
there are other rare causes..
like the engine will not idle at 800 rpm or more.
see this, the alternator goes off line below that much.
and can drain a battery fast deep in the city at infinite red lights
and traffic jams.
that is why getting a car with hands on service by a real ASE
tech, works best , he /she sees all this in 5 min flat.
saving all this grief.
like , oh crud, it idles a 500! (that be it)
or charge lamp is on?
the old jeeps love to kill batteries, with old DC generators
oh my, the OBD2 scan tool says my ALternator is off line.
or other DTC errors, about power lost to many places.
use a scan tool if car is newer.
sad the owner can't tell year or model.