AA exploded a bit in battery case. Replace battery or throw out toy?

It wasn't a lot but the top of the battery wasn't in tact and had yucky stuff coming out of it. I can easily wipe the inside clean of that stuff, it seems well encased in the screwed on batter case. Do I put in new batteries or must I throw out one of my daughter's favorite toys? (Though I don't actually know if it still works.) Also, anyone know what causes this? Thanks!