Cylindrical lithium cell model numbers look cryptic, but they encode everything
you need: chemistry, size, capacity and cell type. Once you can read one, you can
compare any two cells at a glance. Take INR21700-50E as the example.
1. The prefix = chemistry
- INR — NCM (lithium nickel-cobalt-manganese).
- IFR — LiFePO4 (lithium iron phosphate).
- IMR — manganese-based, high-rate.
So INR marks an NCM cell.
2. The first digits = form factor
The digits are the physical size — diameter and height in millimetres. 21700 =
Ø21 × 70 mm. Common formats run from 18650 (Ø18 × 65) and
21700 (Ø21 × 70) through 32700
(Ø32 × 70) up to 4680 (Ø46 × 80).
3. After the dash = capacity
The number after the dash is the rated capacity in units of 100 mAh. -50 =
5000 mAh; -35 = 3500 mAh.
4. The suffix = cell type
The final letter marks what the cell is optimised for:
- D — high-power: high continuous and pulse discharge for tools and traction.
- E — energy-storage: maximum capacity for runtime.
- P — high C-rate: highest discharge current.
- PL — low-temperature: stable discharge in the cold.
- M / MF — high-safety (LMFP / LiFePO4): long life and thermal stability.
So INR21700-50E reads as: an NCM, 21700-format, 5000 mAh, energy-type cell.
Why it matters
Two cells can share a format but behave very differently — a -D and an -E of
the same size trade power for runtime. Match the suffix to your duty cycle, not
just the size and capacity. New to format choice? See
18650 vs 21700, and for chemistry see
NCM vs LiFePO4.
Every model’s full specs — weight, internal resistance, C-rates, cycle life — are on the datasheet. Request specs & a quote →