YouTube user Spiritplumber demonstrates how he built a cell phone charger using four parts from Radio Shack on the store counter immediately after his purchase. The parts cost around ten bucks, and while that's three times cheaper than buying the actual cable at Radio Shack, but how did he know he wouldn't blow out his phone?

The author was not concerned as he knew:

Cheapie wall-wart phone chargers output 5V nominal, but the actual voltage varies wildly, going as far high as six volts and usually stabilizing between 5 and 5.5 volts while under load. Cell phone manufacturers know this and design some tolerance into the phones. A silicon diode drops around 0.7 volts (it's actually a curve: look up any datasheet) from the roughly 6V from the batteries, which brings us nicely where we want to be — the little bit of extra voltage is handy in that it allows partially depleted batteries to still work with this circuit.

You'll need a 1-amp diode rectifier, a 4-battery holder, an adapter plug for your phone, and electrical tape. You can get these in any electronics hobby store (and way cheaper online of course), but since Radio Shacks can be found anywhere it's a good place to go in a pinch. See the source link below if you're curious to see the circuit schematic or want more technical information.


Ersatz Battery Booster | Robots Everywhere via Hack-a-Day