How my Batches can be so high? Like 40 000 batches.

Hello, Im making a terrain with some trees, houses and grass. In some zones the game runs sofftly at 60 frames. The problem is sometimes, inexplicable, my batches goes up to 40000 batches, and the fps goes down to 10 ou 15. And the zones when this happens have the same amount of trees and grass as the other zone where this not happen. Thanks.