So I just finally upgraded from my old phone to a real camera because my sister is getting married in New Jersey next month and I really want to take some good photos of her and my new nephew. I saved up forever and got the Canon EOS 5D Mark IV because everyone said it was a beast but honestly it feels so heavy in my hands already lol. I was watching some YouTube videos and saw these pro photographers using these big plastic blocks attached to the bottom of their cameras and I think they called them battery grips? I have no idea where to start with this and I'm really sorry if this is a super basic question but I'm just so confused by all the options out there.

Like my logic was that I just buy the one Canon makes because it matches the camera but then I looked at the price tag for the BG-E20 and wow it is way more expensive than I thought it would be. Like $200 or something? My budget is already kinda tight after buying the lens and everything so I saw these other ones on Amazon like from Neewer or Vello that are way cheaper but I'm scared they might fry my new camera or something crazy like that. Do the off-brand ones actually work the same way? I really want the extra shutter button for when I'm taking portrait shots because turning my wrist all the way around feels really awkward and I'm worried I'm gonna drop the whole thing.

Plus I heard you can put two batteries in them which sounds great because I don't want to run out of juice in the middle of the ceremony. Does it make the camera way heavier? Is there a specific one that you guys think is the absolute best for a beginner like me who just wants something reliable? I'm just so excited to start shooting but I don't want to waste money on something that breaks in a week...