How to correctly update batch according to post.id

You have ID column in your ci_terms_relationship table. Use that id. 

If this does not work for you you can implement your own batch update function. 
Tutorial is here: https://github.com/bcit-ci/CodeIgniter/w...se-Drivers

It would be better if you copy update_batch function from system folder and then change it (don't forgot to rename it) for your needs