Intro: Big Phone Battery
Run a smart phone directly from a car battery and/or solar panel. Useful if the USB charging port is broken. Or you need a huge cellphone batty.
For 6 bucks you can get an old smartphone online using Ting --
Step 1: 12volt to 3.7volt DC-to-DC Converter
The cell phone battery gives 3.7volts. So you need a 12volt to 3.7volt DC-to-DC converter.
Step 2: 'trick' the Phone Into Thinking It Has a Battery
Cell phone batteries are fancy. They usually have a built in thermistor. You can replicate this using some resistors. You can figure this out by measuring the resistance between each terminal of a cell phone battery.
Step 3: Video
Here is a little video. For proof.
Step 4: All Wired Up
The wiring goes like this:
Solar panel (~16Volts) -> solar charger controller (goes from ~16 volts to 12 volts)
->car battery (12volts) -> DC/DC converter (12V to 3.7V) -> phone battery terminals.
Step 5: 3.7 Volts
A regular cell phone battery will range from around 3.4V to 4.2V.
3.7 is towards the middle, so you won't get a full battery symbol.