I've kept it on terrace for a couple of hours with Drive app on. Ok, there's a building but 5230 next to N9 got the fix in 15 seconds. Then a few hours during hiking and half an hour drive phone in the windscreen cradle, no charger.

But wait, the full story: the phone is a bargain from Amazon, a New York based company selling obviously a stock of Vietnamese branded N9's (yeah, I wanted so badly to have one stupid me). It was v1.2, I changed the product code to France where I live and flashed both the system and the country contents with v1.3.

Could there be some Southern hemisphere adjustments (this is a pure guess) in GPS receiver firmware? Maybe there's an image for flashing that part...