This was already answered. Hooking anything to the battery terminals when the panel has no power will likely damage the panel. You would need the primary source connected before you hook anything to it, and if you attempted to hook your power supply to it while plugged in, it would cause some serious problems to the panel and power supply.
In my opinion, you should learn a lot more about electricity before touching your panel with anything shorter than an 80ft pole. I would recommend reading this: <URL url="So you want to buy a FACP...]