Samsung SDI INR21700-50E

A 4.9 Ah 21700 cell rated for 9.8 A continuous, with the figures a pack design depends on and what each one was checked against.

Where these figures come from

Capacity and nominal voltage confirmed against the manufacturer datasheet. Continuous discharge and internal resistance are published typicals.

What it is for

A capacity cell, not a power cell. Excellent for a low-drain pack that must last; it will be the limiting factor the moment the load rises.

• Capacity: 4.9 Ah
• Nominal voltage: 3.6 V (2.5 V to 4.2 V)
• Continuous discharge: 9.8 A — 2.0C
• Internal resistance: 0.024 Ω
• Mass: 69.5 g

Questions

What is C-rate?

Current expressed as a multiple of capacity. A 3 Ah cell at 3 A is 1C; the same cell at 15 A is 5C. It is the number that decides whether a cell is being used gently or punished, and the rating that matters is the one on that cell’s own datasheet rather than a rule of thumb.

Do you recommend where to buy cells?

Not currently. Every cell page links to the manufacturer’s datasheet and nothing else. If supplier links are ever added they will be disclosed on the page, and the ranking will still be computed from electrical fit alone — a designer that recommends the cell paying the most commission is worthless, and it would look exactly like one that does not.