The battery capacity 1400,1600mah are actually same.
They just advertise that way. The battery cell capacity is pretty much same.
Lithium cells are same. only difference is Li-po but still close.
The 7.4V in 1500mah batteries are sold very good prices in e-bay.
I bought those with charger in a good price last week.
Most of low price of pructs are delivered from Hong Kong/China, therefore the delivery time takes 3-4 weeks.
Check the estimate time for the product. Or search in a website for vx-7r batteries.
You will see a lot in domestic with a faster delivery(3-5 working days) but must pay more.
I actually don't care of 1400-1700mah because no difference.
They can make 3000mah(3.7V in serial) or 1500mah(7.4V in pararall)