Li-Ion vs Li-Poly For Quads
There's a few things wrong here:

1) A $10 charger is a bad idea, unless it's a trickle charger through the balance leads.

2) A $25 prismatic high-C lipo is a very different beast than 18650s, barring very specific ones (the LG HG2, Sony VTC5, etc) and very specific flight modes (minimum time-in-the-air of 30 minutes or longer).  Most 18650s are sub-1C discharge ratings.

3) You need to spot-weld the tabs to the batteries.  Do not solder them.

You also didn't say what kind of 18650s you already have.