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. The two
cylindrical formats we build are 18650 (Ø18 × 65 mm) and
21700 (Ø21 × 70 mm). So 18650 = Ø18 × 65 mm and 21700
= Ø21 × 70 mm — the leading digits give diameter, the rest the height.
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.
- C — 3C digital: balanced 4C-class discharge for consumer and digital devices.
- T — ultra-high-rate: 15C-class burst discharge for drones and FPV.
- PL — low-temperature: stable discharge in the cold.
- M / MF — high-safety (LMFP-blend cathode): long life and thermal stability.
So INR21700-50E reads as: an NCM, 21700-format, 5000 mAh, energy-type cell. Our
own 21700 line uses exactly this suffix system — D, E, C, P and T for the NCM
variants, plus MF for the LMFP-blend cells — so once you can read the suffix you
can navigate the whole catalogue.
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 →