18650 Cells

https://www.google.com/search?q=18650+cells&client=ubuntu&hs=KUs&source=univ&tbm=shop&tbo=u&sa=X&ved=0ahUKEwj8xPLHwdLfAhULtIMKHTQ3ADUQsxgIKw&biw=1438&bih=738

General Performance

• 10A discharge, self-protection circuit inside.
• 3.7V
• 3 Ahr
• 18 minutes of 37W
• 10W for 1 hour
• 100 of these give 1 kWhr
• 45g each, so 1 kWhr weighs 4.5 kg.
• At this density, ultra light cars (500 lb total) - will have 30 miles per kwhr.
• 1kwhr ~ 4MJ - so about 1/10 kg gasoline. Given gas is 20% efficient in cars, we have 1/2 kg equivalent. Tbis gets us to about 240 mpg equivalent.
• With 1 kW solar added- that gets us to about 400 mpg equivalent.

Discharge Characteristics

• Can 18650 cells really discharge at 10A rate? Yes! [1] - Panasonic goes up to 20 amp rate. 6S (6 cell) packs are 22v. 10 of these, if discharged at 20A, give a 200A welder for 6 minutes. See Discharge Rate.
• Crappy ones can be as low as delivering 2.5A each - [2]. With 100 of these, that's still a 250A welder which has a weight of 5 kg for the batteries. Still impressive.

Specs

• Note actual spec from a buyer on Amazon - [3]

Reviews

• https://thegunzone.com/best-18650-batteries/
• https://www.18650batterystore.com/Best-18650-Battery-Guide-s/142.htm

Management

• While specs say 250 cycles for 15A discharge - Multiple thousands of cycles are possible when charged to 80% and drained to 30%. - [4]

Cost

• From <$1 to $7 each - so choose wisely -
• Cheapest - [5]
• Best - Samsung 30Q - 3000 mAh - $3 in bulk - [6]

• These appear to be on spec at 3000 mAh - [7].
• Cycle life and specs - [8] - 250 cycles to 70% of rated
• 1000 cycles at 6A discharge rate bottoming at about 60% capacity for 2000 cycles? - [9]. So these last pretty long.

External Links

• Fantastic forms for recycling old 18650s into DIY Power Walls https://secondlifestorage.com/index.php