CHARGER WONT START UNLESS JUMPED

2007 dodge charger RT, V8 5.7L, Police interceptor package. 133k miles on dash, but just did a engine swap, and has 78k miles on it.

So, before you all ask, yes i changed the alternator, and yes i changed the battery, and yes the battery cables are grounded correctly. It’s weird because when the car is on, and jumped, it stays on, but after 10-20seconds the lights on the dash start going DIM and all the lights just start flickering and going crazy. If i can upload a problem of what’s happening i would. Let me know how to do that, and if anyone knows anything? I did check the rear fuses and some are bent, but which fuses in the rear compartment near battery actually matter, and can show you show me a picture or diagram of which one’s actually matter. Thanks in advance.