In the new gym system right before you start a battle against a defending Pokémon with with your own it shows the two Pokémon, their respective combat powers and battles won. How does the new battles won accumulate? Obviously every battle won increases the number, but do battles won when attacking and defending count? If a defending Pokémon beats multiple Pokémon in a row will it count as one or multiple battles and vice versa for attacking Pokémon? Do defeating raid Pokémon count? Also is the count still unique to a Pokémon when it is evolved?
The question is different from the former gym system (What does "Battles Won" refer to?) because it showed only the battles won by a defender when it defended a certain gym the time it was undefeated. Then a good gym could have Pokémon with about at best over 10 battles won. Now I've seen Pokémon with battles won count exceeding 900! Also when I attacked a gym every time my own Pokémon defeated the gym Pokémon the count went up.
Best Answer
Based on personal experience (and your own, it sounds like), the Battles Won stat now refers to the number of times it has been on an attacking team that has defeated a Pokémon in gym battles. This number used to represent how many times it defeated the last Pokémon of an attacking player's entire team it defeated, but this was changed during the gym rework.
From this Reddit thread: