The battery was replaced brand new but after a day it was completely dead. Something is draining the battery's power. What could be the problem?

 

did you install an aftermarket stereo? something big would have to be on to drain a new battery in 1 day. maybe your amps? or you could have something grounding out in the charging system and shorting the battery in which case the battery may be dead. or you could be not charging have you had the alternator checked out? otherwise it could be any little electrical failure.

 

^ +1 on all that was said above. Was gonna say the exact same thing, either some sort of aftermarket stereo/amps, or alternator.

 

check your alternator first. stereo would accelerate the process if the alternator was dying or dead

 

It's not an aftermarket problem since it's completely stock. I'll check that out, thanks.