I've written a Windows CE app, which will also run on a Windows Mobile 5 and 6 device, to display data from the Paktrakr. It reads the data from a bluetooth adapter on the serial cable. I've got it running on a dashboard mounted GPS. On the main tab it displays amps, volts, temp, soc% and kWh. And on the second tab it has a bar chart of the batteries or cells with voltages. It has a simulation mode and can log data to the SD card.
Display:
The application should also run on any Windows CE 5.0 Core device with bluetooth including the Magellan Maestro 4250 and the Mio C520. These devices may, however, require renaming some of the installed files.
USB:
There is only one USB port on this type of device and it doesn't provide power. So it can't power a serial to USB adapter. Even more, because of limited battery on the device the USB is needed for charging. Perhaps there is a USB splitter that would charge from one side and communicate from the other, but I couldn't find one.
Bluetooth:
The device doesn't have pairing software for remote bluetooth devices so I had to discover devices and open a stream to the bluetooth device directly instead of through a virtual COM port. I used a IOGEAR Serial to Bluetooth adapter that has an AC power cable (output is 5V and .35A). To get it to work on the Paktrakr serial cable. Hopefully I can find a car adapter to fit it. Then I had to solder a wire between pin4 and pin7 on the 9pin serial cable coming from the paktrakr.
While this wasn't an ideal solution it does work.
Better Bluetooth Cable:
I ordered a couple bluetooth usb dongles from Amazon for 99 cents each. They run the Broadcom 2045 chipset which has very low power requirements. So, I believe it wouldn't be too hard or expensive to build a cable from Paktrakr. I'll be looking for some help with this since it is out of my comfort zone.
GPS:
Microsoft has a GPS Intermediate Driver (GPSID) that is available on Windows Mobile 5 and later. This allows multiple apps to share the GPS hardware. This GPS device doesn't ship with GPSID and I can't find a way to set it up. So, watthour/mile will have to wait for the "advanced" version.