we talked about this for the N900.

Quick explaining:
Voltage curve for Li-ion/LiPo battery's is not linear, and the voltage drop from goes pretty fast from 100% to 90% compared to 80%-50%.
^^ - just some info on battery voltage

But main thing is your charger almost never goes to 100% because this actually let your battery live longer, it charges normally to 4.15V-4.20V and 4.23V is 100%.

Hope this helps, else there are plenty of battery pages on the net or go through some pages in my battery thread or other thread's for the N900 about the same "problem"

so again nothing wrong here, just a good practice for letting you battery's last abit longer, + you will not get much out of the last few % anyway.