Except two 14500 stacked in series would give you around 7.4 volts. LiIon batteries generally charge up to a bit higher than the nominal rating of 3.7 v, drop of quickly, and flatten off until they are about to be fully discharged.
Your mod-whatever it is- must have some sort of resitance or regulated circuit to drop the voltage back down. If it's regulated, a single battery at 3.7v won't even trigger the circuit. If it is a resistor, then your voltage would be 1/2 of 3.7 v.
You still have to short the space taken up by the second battery
Now, you should be totally confused.