Worth 1 Victory Point for each differently named Victory card which you have no fewer copies of in your deck than any other player.
This is a Victory card and does nothing until the end of the game, at which time it provides an amount of Victory Points determined by the number and types of Victory cards each player has accumulated.
When the final victory point scores are calculated, group your Victory cards by name and compare them to the number of cards in the same grouping that each other player has. Compare cards in the standard Supply as well as all Kingdom cards which are Victory cards, including Battlefield itself.
For each of these groups of Victory cards, if you have an equal or greater number than any other player, each of your Battlefields are worth one additional Victory Point. For example, if you have equal or more Estates and Battlefields than any other player, your Battlefields would be worth 2 Victory Points each.
It is possible for your Battlefields to be worth 0 Victory Points if at least one other player has a higher number of Victory cards of each name than you do.
The total Victory Point score or total number of Victory cards is not a factor, only the number of cards in each group that each player has.