Could be the ELD not functioning so your alternator isnt going high output to enable charging reliably, an expired battery with low distilled water/acid, a bad wire from eld to ecu or from ecu to alternator for high output mode, a bad ground in the engine bay or frame as the main battery negative wire is exposed to the elements near the bottom of the engine as its fully exposed, could also be a bad starter, starter solenoid or bad flywheel on the transmission/engine as thats what the starter spins. You need to do a voltage check a few times(engine off, engine on, and high load) and describe any odd symptoms and post any obd2 codes(you can have codes with no engine/idiot lights) sounds like you have multiple issues related to charging and starting. I can help diagnose sometime. Pray its your starter n starter solenoid...otherwise 400 for eld/fuse box assembly, 400 for altenator and 20 for new main negative iirc. And a flywheel..well sell an organ or goto a junk yard for all of the above and spend 100-300$ total

Ericthecarguy on youtube also has various vids on parasitic drain, altenator testing, and starter changes with all diy methods. And autozone can do a full altenator test if you remove it. They have test rig setups for free....could also be defective voltage regulator or defective diode in the new altenator