I have one of these as well...and I'm not sure what the deal is ( I think it's defective actually), but it has a REALLY hard time getting a satellite fix in my car. In the front windshield, it works ok, anywhere else results in no sats at all. Even in the garage, nothing. And when it runs dead and the pc comes back on, the 818x will turn charge enough to turn on and then shut back off when the battery is drained. Does this continually until it has a good charge...which makes it next to useless to just jump in enter a destination and drive.
So I ordered a Canmore 730f to tide me over until I get a replacement. Come to find out...if you download the software from Canmore themselves...you can not only set the serial port baudrate all the way up to 230k...but you can set the position update rate from 1-10hz. I thought it couldn't possibly be true...but at 10hz the nmea data going by is just a blur and setting the update rate to a slower speed shows a slower speed of nmea data scrolling. So apparently it does do faster rates than 1hz.
The other thing I noticed in Canmore's software looked like the option to update the firmware on the gps receiver. Haven't seen that on other ones.
I paid $25 w/free shipping. Bought a second one since it was cheap and worked good. Going to use it in my wife's setup.
Does your vehicle have tinted windows? Mine does...and what's strange is that it worked FLAWLESSLY when I lived in Missouri. I had a globaltop g33 bluetooth that sat on the back speaker deck and then this 818x and both worked like champs. We moved to Houston and a few short months after, neither one will pick up on the rear speaker deck anymore, but pick up fine on the dash under the windshield or outside the car. Bizarre.