Cheap DIY iPhone External Battery
The beauty of this design is that you can take a box of AA batteries with you on a trip and not have to worry about your phone dying and you can buy AA batteries just about anywhere.
Use your existing docking cable to connect the iPhone to the battery. I prefer this method to the one where the battery attaches to the phone directly. The battery can be in your pocket or purse while you use your phone normally with just the cable connected to it.
Caveat: I did this and tested it on my first generation iPhone!!! Should work on new 3G iPhone but I haven’t even seen one yet.
You could also buy a cable from Amazon.com or cablestogo.com and cut off the male end. (OUCH)
Now you would think that all I needed to do was connect the Red (VCC) and Black (GND) to the battery and it would be done. I tried that and it didn’t work.
To make a long story short, the iPhone wants to see some voltage on the data pins or it will not start charging. I created a voltage divider with a couple of huge resistors (100K) and tied both data pins to the junction which yields half of the battery voltage which seems to satisfy the iPhone. The current drawn by those two 100K resistor is 30 microamps at 6V.
Here is the finished product. I pasted the diagram on the box because 2 weeks from now I won’t remember what the hell I did to make it work!
I suggest you turn off the off the switch on the battery holder when not in use to prevent the resistor divider from draining the the batteries. (Do not despair if you don’t have an on/off switch, it will take a long time to drain the batteries with a 30 microamp load.)
WARNING: There are no guarantees and I will not be held responsible for you damaging your phone. I only tried this with my phone using 4 NiMH batteries that were putting out about 5.2 volts.
I would love to hear from you if you found this article useful or if I made a glaring misteak!?!