Welcome!
Quite a long time my faithful mobile companion was the Nokia N82. Once he suddenly sat down, and charge it anywhere. I bought a battery for 300 rubles and was satisfied.
After some time, he was holding a charge less and less. Was bought new original battery and I stopped using the batteries for the 300r, but nothing has changed. Phone as sat for an hour listening to the music and sat down.
I think the problem is in the definition of charge of the battery probably lost some calibration in the phone, because I already tried to change the battery and nothing changed.
Poryskav on the Internet, found a method of calibrating the battery — but it's pretty doubtful.
Maybe someone knows the reason why, over time, almost all phones (with an iPhone so the effect is less) starting unjustified less "hold" a charge and do not adequately show the battery level? And battery replacement does not help.
And how it can be connected with the installation of non-standard batteries?