Battlegrounds incorporate "match making ranking" aka MMR. I believe this is per character, not per account. The more experience a character has in BGs, the higher your MMR becomes. The game attempts to match you with players of equal MMR when you queue for a BG. In other words, you're up against equally experienced or inexperienced players as the case may be. I do not know exactly how ZOS determine this. I imagine if a character is below 50 or very low CP, say below CP160, they take that into account. However basically it's based on how many BGs a character has done and, perhaps, what kind of success you've had.

When you're new to PvP you may notice that Cyrodiil and Imperial City offer stiffer competition. You may find the competition in the no CP campaign (Ravenwatch) a little easier. Many lower CP players go there. If going there, research what armor sets are allowed since, unlike BGs, that's also a "no proc" campaign.

That said, during the current event everywhere is very busy. This cuts both ways. On the one hand there's lots of action and you'll be attacked from all sides (beware of bombers). On the other hand there are lots of less experienced PvPers participating in every campaign.