Battle Pets are a fresh experiment in ArcheAge added during CBT5 phase, they weren't present before.
Generally, all the usual mounts can be used as pets for attacking, but they are significantly weaker than the battle pets. Both pet types have the same character screen and use the same equipment, but battle pets have different active skills. Mounts can be obtained from a level 5 quest, Battle pets from a level 25 quest.
In CBT5 only one type of battle pet was available for testing, which was the Wolf. There were 3 types of wolves in CBT5, different only in color. Here is a video showing how to raising a baby wolf, a fast progress.
I found this quite interesting, especially the fact that your mounts can also be your pets.
The last stage of ArcheAge’s journey to launch on September 16 begins this week! Head Start, our four-day pre-launch event, kicks off this week on Friday, September 12 at 10:00 AM PDT (GMT-7) and running until 8:00 AM PDT (GMT-7) on Tuesday, September 16!