Building my own portable battery pack...

I've done this, though I used it for:
a) Charging my phone at Download Fest last year and this year
b) Charging a G1 phone used by volunteers collecting smartphone sensor data (including GPS location and satellite data) for my dissertation on long multi-mode journeys.

The pictures show it all really - 4x AA cells in series hooked up to a USB hub, allowing up to four USB devices to be powered.

Picture 1: http://twitpic.com/3qjv1y

Picture 2: http://twitpic.com/52xa3u
 
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Looks interesting! Is that battery pack just fed straight into the USB Hub's power port?

Where does that input USB plug come from? (or is that just another output?)
 
Use one of the battery packs above, the Trent iCruiser looks good. I have an app called GPS logger, from Android Mkt, and you can set the GPS acquisition time yourself, longer between acquisitions = better battery life. I used it while on Safari in April and while out all day the battery was drained about 75% but I did have 3G on too as I was loading maps at some points.

Alternatively a Garmin Edge 500 would do the job too and they have quite good battery lives. Check out bikemap.net too
 
Yeah, the hub just gets given 6V. Haven't had any problems.

In the second picture, the USB cable on the left is a device being powered, while the USB cable on the right is just the downstream connector for the hub (i.e. what you would normally plug into the computer). The hub end is permanently connected, and rather than destroy the hub's data multiplexing ability by cutting it off, I've just coiled it up and plugged it into one of the ports to keep it tidy.
 
Could have been better, could have been worse. I haven't really used it enough times to know for sure, but I reckon I got somewhere between one and two charges of the HTC Hero extended battery (2200mAh if I remember rightly, or it might have been 1600mAh) out of one battery of cells at Download Festival this year. So it could be expensive to run long term, unless you use rechargeables. The charge rate was decent though, the same as you'd expect from mains if I remember rightly.

The biggest problem though is that the hub doesn't seem to have any low supply voltage cut-off mechanism, so when the AA battery voltage drops below a certain point (presumably 3.7V) the phone battery stops actually increasing in charge level, even though it will still claim to be "charging".

The work around was just to check the rate of charge in % per 10 minutes or similar, and replace when that fell. I checked the batteries were dead by putting them in my LED torch, which has a higher, more sensible voltage threshold at which it will not light (as strangely enough I didn't take a multimeter to a music festival!).
 
tim80bwi said:
I could build a regulator, I'd just rather I didn't have to :p The car charger accepts a 10-30V input and outputs 5V USB, so seems perfect for an easy bodge. I just need to get the battery/capacity choice right for the input.
Click to expand...

11.1v 5700mAh LiPo. That, balancer (Essential) and charger (plugs into charger) should be about 40 on a popular auction site. By far the best energy density of anything out there at the moment. Chuck it in a box with your adaptor, and hey presto.
 
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