The three interesting properties of a single cell lipo battery are:
- capacity (mah)
- discharge rate (C, A)
Capacity refers to the total amount of energy that can be stored in the battery,
discharge rate to the accessibility of that energy.
The discharge rate in C, multiplied be the capacity, gives you the discharge current in A(mpere).
If you want to fly fast, look for the best discharge current:weight ratio.
If you want to fly long, look for the best capacity:weight ratio
Be aware, battery labels are sometimes.. erm.. a little inaccurate.
Only the weight, trust you can!
Depending on motor size and drive type,
here are recommendations for battery weight (popular RTFs as reference):
CL-0615 motors in direct drive (e.g. Nano QX): 4-6g
CL-0615 in geared drive (e.g. Syma X11): 5-10g
CL-0720 in direct drive (e.g. Hubsan 107L): 8-15g
CL-0720 in geared drive (e.g. Syma X5C): 10-20g
CL-0820 in direct drive (e.g. Hubsan 107C/D): 12-20g
CL-0820 in geared drive (e.g. Blade 180QX): 15-25g
Once you have determined your target weight, compare a few batteries with the simlar weight and divide cash you spent for each pack by amount of BS on label and determine the "$$:BS" rate to conclude the F rating (fun factor).
Search for the vendor with highest F rating and stick to'em!