You need to know the classic electrical saying, in series volts add while amperage stays the same, whereas in parallel amps add while voltage stay the same.
So, by putting four 300Ah,12V batteries in series, you get 300Ah at 48V. That works out to be 300Ah X 48V = 14,400Wh
If instead, you wired those four 300Ah,12V batteries in parallel, you'd get 1200Ah at 12V. That works out to be 1200Ah X 12V = 14,400Wh.
So, to answer your question, you'd need 2 parallel strings of four batteries each (that 4S2P) to give you ~29kWh of power.