a cosmos db is made up of partitions. each partition may be on separate server. atomically updating two partitions would require cross server two phase commit, and would break the Comos DB response time commitments.
as a Transaction Batch is an atomic operator by definition, it can not cross partitions. if you don't need an atomic transaction, then
you don't specify your requirements. you could write a cosmos db stored procedure that you passed the batch items to, and it could insert non-atomically.
note: stored process are easier to write, if you create async wrappers for the api calls. see: