Portable battery packs for your smartphone or tablet are handy. You could buy one, but you can save money by making your own.
Newer devices can draw a lot of power -- so a bigger case can get you more juice. Lenmar Enterprises' guide uses a plastic bar soap container instead of the small tin and is much easier to make to boot. The plastic container closes tight and can hold more batteries.
Check the video for full details.
DIY: Make your own portable battery pack [YouTube]