power adapter for GPS logger ....plz HELP

Hi,

I want to build a Power adapter for USB GPS logger. A little info about the GPS, the GPS logs data when it is connected to USB power source (PC/laptop). The device has built in memory to record the data .I don’t want to carry laptop when I am hiking. According to user manual of the GPS
Power Consumption: < 42mA (1Hz standard version)
Input Voltage: 3.8~8V DC

So my questions are …
1. Is it possible to use a 3.6v cell phone battery( Motorola phone), with a volt regulator or not, to power the device? how long it will last
2. If use a 9v and volt regulator and how long it will last.

If the answer is 1 then how can I find out the + - of a USB cable to power the device or if it is 2 then more work and how to build a power adapter and what kind of volt regulator I can use . Where can I get a volt regulator from NOT from store caz I got lot of broken PC and laptop main boards. I hope anyone who s reading understand my Qs. Thank You very much in advance 

NOTE:I don’t very much abut electronics

Hi, the GPS has an internal voltage regulator. A 9v battery wont suit as 42mA it wont run for long at all. I would use 4x AA battery pack, which is 6v-5v over the life of the batteries which suits fine and pretty good life (guestimate 24+ hours).

You can get a 4x AA battery holder from anywhere for a couple bucks and use a USB socket from one of your junked PCs.

THanks Mr.RB