Batteries
For 4s1p - shrinking tube should be 90mm - 21700 is 21mm*4 Good sources: Complete Guide for Tech Beginners : 14 Steps (with Pictures) - Instructables Connecting the Dots: Series vs. Parallel Circuits (recurrentauto.com) To solder 18650 or 21700 batteries, ideally, you need a spot welder, on amazon, they cost arround 50€. You also need balance leads and positive/negative leads. Buy option: Molicel INR21700-P45B 4500mAh - 45A - 21700 & 20700 - Li-ion - Rechargeable batteries | NKON Series lipos: example for 2S (1S added to another 1S): If we take two batteries of 3.7v, 2000mah each, and connect them in series, you will get a new battery of 7.4v, 2200mah's. 3.7 v is the storage voltage, for a lipo, if charged, it would be 4.2volts and 2200mah's We keep the amount of mah's. Paralell