Yeah I tried one of those battery powered external GPS a few years ago - the sample rate is junk and they also lose power. I should be clear that what I have is a hard wired external antenna for the Racelogic device, which is about as accurate as you’re going to get in a civilian owned vehicle. It doesn’t work near buildings but it’s great at an open track. I basically wanted the Racelogic stowed away with a power wire instead of suctioned to the windshield.
antenna
http://www.amazon.com/gp/product/B00GCBA2EK?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00
vbox
http://www.amazon.com/gp/product/B00GC3BMDS?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00
BT OBDII
http://www.amazon.com/gp/product/B0061XSX0O?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00