First , this 750mah battery has both a Syma stk and a JST pigtail on it.
Discharge specs ,, 750 nanotech battery - Discharge 726ma , 370 sec's to 3.7 volts.
600 nanotech battery - Discharge 570ma , 225 sec's to 3.7 volts
650 upgrade battery - Discharge 582ma , 200 sec's to 3.7 volts " low voltage "
600 Tiger stick batt - Discharge 520 ma , 115 ! sec's to 3.7 volts
500 stk Syma battery- Discharge 482 ma, 190 sec's to 3.7 volts
These were all charged at a 2C rate and a 3 Amp discharge to a cut off voltage of 3.30 volts.
The Turnigy 750 nanotech is the clear choice if you want the highest run time and flight power "voltage " BUT some may be frustrated by the extremely tight fit.
I'll still say as I have before that the 500 stock Syma batteries are great for a 500 mah cell.
NOTE :::: THE 600 MAH NANOTECH IS NOT RECOMENDED FOR THE SYMA X5 AS IT REQUIRES EXTENSIVE MODIFICATIONS TO THE QUAD TO FIT AS ITS A MUCH LONGER BATTERY
Read below as I've found that the Dromida 700 is a great option for power and additional run time.