References for various fundamental things - composition, balance of details etc. I don't have sources for most of these as its something that was lying on my hdd for a while, but you should be able to look it up through google images.
SingFire SF-B08 8800mAh 8.4V Li-ion Battery Pack for T6 U2 P7 Bike light lamp - (8 x 18650) — 1628.56 руб. — The battery pack is consisting of 8 x 18650 batteries with large capacity long operation time. Interface is 5.5 x 2.5mm