Briggs, sorry man... jumped the gun on you, was tad irritated by your droid post.
Here's the info you were discussing from an old post of mine 2010.
http://forum.ppcgeeks.com/htc-touch-...usb-power.html
The link under
"B" (battery) in wiki #5 disappeared & the other link with it in, was bad... fixed now...
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The key is the amperage/amps/ or ma (milliamps) or mah (milliamp hours)
On full brightness that may suck up 350 ma just by itself not running anything!
Charging Batteries Using USB Power
All host USB host devices like
PCs and notebooks can source at least
500mA, or five "unit loads" per USB socket. In USB terminology, "one unit load" is 100mA. Self-powered USB hubs can also supply five unit loads. Bus-powered USB hubs are guaranteed to supply only 1 unit load (100mA).
Charging Batteries Using USB Power - Maxim
……So, if your phone is sucking down 600 miliamps running wifirouter & GPS & other apps.. your battery will not only ‘not charge’ while plugged into your laptop/pc, it’ll eventually die!
“Besides a data link, USB provides 5 +/- 0.25 volts to power an otherwise unpowered device or charge a battery in a self powered device. A USB controller or hub is required to power one unit load (100 mA, a low power load). It can optionally power up to 5 unit loads (500 mA, a high power load). The spec is silent about intermediate loads, so I assume that the sources deal with just the two cases. Either a load is low power (like a keyboard or a mouse) or high power (like an iPod or PDA).”
USB As A Power Source
Q&A:
Q: “but it sometimes works”… “I plugged it into my car & it didn’t die for the whole trip last time…” etc.. etc..
A: If your phone battery was full as opposed to almost out & one trip you ran GPS the whole time, it makes a difference.
Q: Sometimes the charger may say only how many watts it produces…
A:
Power P = I × V = (Watts = Amps x V) : Amps=Watts/V : So if the charger at the store says it’ll do 2 watts… Amps = 2/5v, = .4 amps or 400 ma, not enough!
Q: Can I use a 500 ma charger?
A: Sure, should be enough 80% of the time! But, there is a reason HTC sends a 1amp charger when you buy the phone.. it’s possible if you have the screen on full & the program (GPS map) is using a lot of bright colors & the gps chip is running & you’ve got another couple programs in the background and your talking on the phone and your battery was at 2 % when you started… you may be drawing 700 milli amps.. then logically it’s only a matter of time until your battery dies & the charger isn’t putting out enough to keep the phone running & it shuts off. And if the charger it is putting out just barely enough to charge the phone, it will take forever to charge the battery!
Q: I’m using a USB charger from my old phone & it works some of the time…
A: Sure, a 350 ma (output) charger will charge your phone fully if it’s left overnight (it usually goes into sleep mode & is drawing almost no power).