I believe that the back cover face to make contacts that make better gps.
Take a test, raised the cover battery covers and try to launch such as tomtom, you will see that no locks satellites or locks them with a very long time and with a low signal, then put the cover and see which links immediately satellites and a high signal, raised again the cover and see the signal of satellites coupled fall relentlessly until you have a signal low or even absent ...
So the problem with the battery increased from 1800 I think that depends on the cover that crushes not something that runs the gps.
Why not cover the gps does not work well?
Sorry for my English ...