It's not a CVT, it's a manual trans that is clutched and shifted electronically.
bayoubelle, there is a must-read thread in the dinghy forum at IRV2.com about the battery disconnect for the Focus. In the thread there are a couple of good ways shown to make it easy and foolproof. Read it to the end, because some of the early posts show solutions that aren't good. No, it won't void the warranty.
When you see how hard it is to disconnect the negative at the battery post, you'll know why people add paraphernalia to make it easier.