i have the Note 3 sm-n900 and have good battery life and im a heavy user too... but i dont if the M8 battery is interchangable like the Note 3 is... being that the Note 3 comes with a 3200mAh battery, i have a backup battery i bought thru ebay that is a 4700mAh battery that is the same size as the OEM one that comes with it. so having a replacement battery (specially a bigger one) is a nice plus... Not even sure if you can even replace the M8 battery, but if so i hope you make a purchase that you can enjoy for a while xD