The short answer is that not all VG models can be imported via BAT. There was another discussion about this last year (that I can't find). We are using CUCM v14SU3 and the 420 is available as a Gateway Template and in the bat.xlt, but not the 400. Unfortunately, I think you are out of luck.
That said, you might be able to build one full out, and then do a Bulk Administration > Import/Export > Export (and choose Gateway for export). Then grab the sample 400 out of the resulting file, and using Excel and or a text editor, create new lines for the other gateways you want to create. Then use Import to import them. For sure test this in a lab and at a small scale first.
I have created objects in bulk in CUCM of many types using this method when I was teaching and had to set up labs. I've not done it with VG400's, so your mileage may vary.
Let us know if you have questions.
Maren