Originally written some time in 2014
So recently, a situation came up where I had to bring wifi to the middle of nowhere. By middle of nowhere I mean no power, no nothing. So I decided to bring along my Linksys WRT54G (Running DDWRT). I have a small battery pack that I built, and I figured I would power the router off that. At first I was just going to bring my inverter and plug the power brick of the router into that. But its pointless to me why you should conver the power from DC -> AC -> DC again. So after my friend on IRC mentioned I could power the router directly from the DC power source. I thought for sure I would need some kind of adapter, but it turns out the router can in fact be plugged directly into the DC power source. So heres the steps below, so you don't have to go though the same guessing game I did.
Step 1: Find an older power adapter that fits your router's power port. Make sure its old, and not the power adapter you need for the router. (Once this is done, you can't use the adapter anymore to plug into the wall).
Step 2: Cut the wire of the adapter.
Step 3: Strip the insulation off the wire. (My picture doesn't show the bare wire, since I put terminals on it so the wires would stay connected to my battery. This is NOT required, you can just touch the bare wire to the battery terminals if you don't have the connectors you need.)
Step 4: Located the positive and negative wire. The positive wire will have a solid white line (As seen in the photo). The negative will have nothing on it. (It could have writing.)
Step 5: Connect the wire to the battery.
Step 6: Plug in the router.
Step 7: ENJOY! Your device is now running off DC power, with no need for an inverter or AC Power source.
This dosen't apply to just my router, in fact anything that runs of a 12v power supply can be powered directly from a DC power source (Such as the battery). This can come in handy when you have to power something in a car or from a battery, and don't want to use an inverter.
Thanks to HeavyMetal in IRC Chat for the idea!