Batch Jobs are designed to change data in "batch" during the import of vehicle information. If you have data that isn't included in the import, e.g. Vehicle Descriptions you will need to modify the process so that current data doesn't get changed.
An example of this would be "Prepending" content to a the Description field. If you were to set it up without using the following process the content would be added every day as you data is updated within a feed.
Step 1) Create your Batch Job
Step 2) Run the Batch Job (one-time)
Step 3) Change the rule of the Batch Job to run on vehicles that are less than 2 days old. So '> 2' in the days in inventory section.
*Note: If you are manually entering all of your data without any feed then Batch Jobs only work when you manually "Run" them. You will still want to set them up as show above to avoid deleting, overwriting, or duplicating the content.