How to correctly update batch according to post.id

Didn't even know update_batch was a thing. Had a quick look at CI documentation, and at first glance it seems ok for couple of records, but the size of the SQL query could potentially spiral out of control very quick with number of records or number of fields to update.

update_batch has $batch_size parameter,default is 100, if there are more the than 100 records it breaks them for clusters with 100 rows. so I think the number of rows will not affect it.
(My English is not good, so I might misunterstood your point)