I have always had the nokia's, I have never had one that can match nokia's advertised "standby time". Nokia's website says my phone should do between 150-300 hours standby, 3-5 hours talk time. If I did just leave the phone in standby and timed how long it would last, I wouldnt expect more than 72 hours out of it. I might only make between 1/2 hour to an hours calls per day, so its not as if Im a heavy user. It could NEVER last 12 days.
With my last phone, cant remember the model, but it was one of the first colour phones put out by nokia, I did try replacing the battery with an aftermarket one off ebay with a higer capacity (few hundred more mAh). It helped a little, but still could never make the hours that nokia claimed.
I havent had a chance to play with the bluetooth on my gps yet, but I did notice that the icon on my phone (normally there is an icon showing when bluetooth is on) disappeared. I went into the menu, tried to turn it off/back on, it wouldnt, just kept saying it was on. Because it wasnt on properly, gps didnt see it. Fix was to turn the phone on/off.