On paper it looks good, about battery being big, not so much because of big screen which is main power consumer. Even if screen is kept off, circuits are probably designed for screen being on and drawing most power from battery because of big screen being key selling feature of this phone.
The thing about amps used in phones, I mean dedicated ones is that power saving and power draw protection because of all other circuits inside phone is main design goals, advertised heavily in such specific mobile amp chip manufacturer's spec sheets.
I read in here the other fellow asking about no distortion and pure sound, well, at one time I started reading all those tech details about amp chips used in phones and what they do to the actual sound going into them, I mean like multi stage AGC, predictive amplification curves steep and not so steep and chip decides what to do depending on input and such that 'kinda' change what comes out of that chip. Also something called speaker coil protection is meant to limit current going into these tiny speakers because their coils might melt or something, looks more like clipping and power overdraw avoidance at all costs, that is given a more fancy description.
If you ask me, these guys designing the chips invent a new way to f...k up mobile phones sound every day.
Their problem is that if amp is allowed to draw too much from battery, even momentarily, then an undervoltage might occur, cause we don't know if the battery is even full or almost empty, and if voltage goes too low then all the other circuits won't like it, also voltages available are very low to begin with and clipping must be avoided because the user will definitely notice that, so all those multi stage AGCs come to play, and the list goes on and on.
Don't get me wrong here, they probably do their best to improvise any possible way for a kinda decent sounding amp to work with almost no power and no serious voltage and not allowed to draw any more power momentarily and must not clip too, and battery must last a long time cause people won't buy the phone otherwise, and yes, must also sound nice, so go solve that if you can.