18650 Cells

What it it?

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.

Best Cell

• Samsung 25R - [1]. 20A continuous for 6 minutes at 3V. 60W cell. 100 of these are 6 kW, which make for a decent burst power source at 4.5 kg weight.

Discharge Characteristics

• Can 18650 cells really discharge at 10A rate? Yes! [2] - Panasonic goes up to 20 amp rate. 6S (6 cell) packs are 22v. 10 of 6s cells, 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 - [3]. With 100 of these, that's still a 250A welder which has a weight of 5 kg for the batteries. Still impressive.
• Discharge rate of 20A yields temp increase to 50C - [4]

Specs

• Note actual spec from a buyer on Amazon - [5]

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%. - [6]

Sourcing

• ~$3 each in packs of 40 - [7]

Cost Analysis

• From <$1 to $7 each - so choose wisely -
• Cheapest - [8]
• Best - Samsung 30Q - 3000 mAh - $3 in bulk - [9]

• These appear to be on spec at 3000 mAh - [10].
• Cycle life and specs - [11] - 250 cycles to 70% of rated
• 1000 cycles at 6A discharge rate bottoming at about 60% capacity for 2000 cycles? - [12]. So these last pretty long.

• From lifetime design perspective, 2000 cycles is only 3 years, though. If used daily - batteries last only 3 years. In practice - 10 year max is likely. Not a good solution environmentally.

20A Continuous

• This one says it's 20A continuous - [13]
• See ratings link for 30A continuous
• 20A continuous and best seller- Samsung 25R 18650 - [14]

Links

• Ratings of 18650 batteries - [15]
• 18650 Cells
• Arduino Battery Chargers
• 18650 Battery Packs
• Battery Pack SMEs

External Links

• Fantastic forms for recycling old 18650s into DIY Power Walls https://secondlifestorage.com/index.php
• Best rated battery and everything you need to know about 18650s - [16]