Can I use this relay to control flow from a DC power source (e.g., battery) as well ?
You might run into some arc issues depending on the voltage and current you plan on switching from the battery. If both voltage and current are low enough you might be okay, however, it would generally be a good ide to use DC rated relays with DC voltage.
Here is a more detailed forum post that goes over using AC relays for DC applications: https://forum.arduino.cc/index.php?topic=470945.0
Hope this helps.