Only the chargers output makes a difference. Example 400mAh or 1200mAh. The 1200mAh charges faster, but if Nokia has make same mistakes than they made with the N900. It will dropout as soon as it hit the 4.15-4.2V and not "calibrate" (slow charge) it to the real full 4.2V.

I notice, that if i charge the Nokia N900 with PC usb (~500mAh). It charged better. It's hard to follow the battery drain of the N9, because there is not free battery-eye and i do not will to pay for that (BatteryGraph). Ohh.. There is the Uptimer. Must collect some battery data.