Comment by gst

Slightly offtopic but related: One of my mobile providers supports configuring public (non firewalled) IP addresses for mobile devices and when choosing that option my phone battery drains very significantly faster than otherwise. I suspect it's because all the random packets that arrive every second or so on the public interface (when NAT and firewall are disabled) either cause the radio to use a lot more battery or prevent the CPU from going into sleep mode (or both of that).