Welcome back!

This a short and simple project, that most likely will be a huge help in a household.
Almost everybody have a USB power-bank at home, for your mobile electronic devices. I can recommend something like this:

http://www.ebay.com/itm/LCD-Smart-Charger-2-3-4X-1...

If you know about the process of salvaging old laptop batteries, this is a great way storing more power without more than one power-bank.

But that aside!
I suddenly stood in a situation where I found out my baby-monitor was not battery powered. And i wanted that..
I couldn't use my power-bank because of two reasons. one: It was DC and not USB, second: It was 6V, not 5V.

Let's begin!

Step 1: Research.

Your device will have a power supply, and on that it will say an OUTPUT voltage and Ampere.

Mine was 6V and 600 mA (0,6A). therefor i needed a step-up from 5V to 6V and it should be capable to run a current of 3,6W. (no problem! but in your case it could be?)

I use this page to calculate:

http://www.rapidtables.com/calc/electric/ohms-law-...

Insert the Voltage and Ampere and press calculate.

Step 2: Electronics

Shopping time!

Step-up (boost converter)

http://www.ebay.com/itm/5PCS-MT3608-2A-DC-DC-Step-...

DC male cable

http://www.ebay.com/itm/10pcs-5-5x2-1mm-Male-DC-Po...

DC adapter set (optional)

http://www.ebay.com/itm/Universal-8-DC-Power-5-5-2...

USB cable (if you don't have any spare laying around)

http://www.ebay.com/itm/New-DIY-USB-2-0-Male-Conne...

If you choose to use a spare USB cable you can most of the time use the picture I attached to find the power and ground wires (+-).

Solder it together like the first picture applies.

Step 3: 3D Printing! Cause Why Not?

If you don't have a 3D printer, it's no problem.
Just find a small box that can fit the electronics, and drill/cut some holes for the cables and the make sure to drill a hole for the screw to adjust the output voltage!

To assemble it just hot glue all the electronics in to the box and screw the lid on. I made the 3D print so you can remove the lid to make a future maintenance if necessary.

Step 4: Finish the Product.

Make sure to measure the output voltage with a voltmeter or a multimeter. See picture to do it an easy way!

Now you can make many of your smaller wall powered electronic devices battery powered!

Have fun! And remember to ask if you have any questions. Comments/improvements on my build is also very appreciated!