Well i tested a bit.
With original battery and cover GPS is good .
When i put on the other cover GPS is still good .
With the 1800mah battery no GPS dont mather with or withour cover.
What i saw is that the originao battery has some small thing beside the battery connectors , i guess thats for the GPS .
The 1800mah battery doesnt have those .
Well the best is to wait for the HTC more powerfull battery .