One option is that you can purchase a backup AA NiMH batteries from here: (http://www.usglobalsat.com/store/p-241-dg100-aa-ni-mh.aspx
). You can also use alkaline batteries; however, if you are going to plug in the DG-100 to the computer, you must remove the batteries first to prevent any damage to the device.
If you want a portable charger, you can possibly utilize the USB Power Bank (http://www.usglobalsat.com/store/p-664-usb-power-bank-charger.aspx
). We have not tested it with the DG-100, but it should work.
Perhaps, it would be better to use the backup AA NiMH batteries or Alkaline batteries, but they need to be initially removed before the unit is plugged into the PC.