18650 is a 2400 mAh battery that works at 3.7v. RCR123A are 3 volt
batteries and are a lot smaller than the 18650. People are using two RCR123As to vape at 6 volts.
For the RCR123As, the 750 mah are LiFePO4 batteries. These are said to have a safer chemical makeup. The 900 mAh are Li-Ion protected batteries. Not sure there's any noticable difference for
vaping. I've been using LiFePO4s for a couple of months now and love 6V.
And I'm sure someone much more knowledgable then I will be along soon.
