Li-ion
18650 vs 21700 Li-ion for Drones: Which Cells, Which Packs and Why
Li-ion cells store more energy per gram than LiPo but give it up more slowly, which is exactly the trade a long-range or endurance drone wants. This guide compares the two common cell formats, explains the Molicel numbers everyone quotes, and shows how a drone pack is built.
Published 24 September 2026 · by the Fioparts team, Gurugram
Li-ion vs LiPo: why long-range pilots switch
Both are lithium chemistries; the difference is packaging and priorities. A LiPo pouch cell is optimised for current — it will dump 100 A into a set of motors without complaint. A cylindrical Li-ion cell is optimised for energy: around 250 Wh per kilogram against roughly 150–200 Wh/kg for a hobby LiPo, so the same weight carries 30–50% more flight time. The cost is current delivery — a good 21700 cell gives 30–45 A, a good 18650 10–35 A — and a flatter voltage curve that sags under punch-outs.
That trade suits a drone that cruises: a 7″ long-range quad at 15–25 A total, a fixed-wing, a mapping platform, a cinelifter loitering for a shot. It does not suit a 5″ freestyle quad that pulls 80 A at full throttle and expects it back instantly. Rule of thumb: if you spend most of the flight below one-third throttle, Li-ion will fly you further.
18650 vs 21700: the cell formats
| 18650 | 21700 | |
|---|---|---|
| Size | 18 mm × 65 mm | 21 mm × 70 mm |
| Weight | ≈ 45–48 g | ≈ 65–70 g |
| Capacity (high-drain cells) | 2500–3500 mAh | 4000–5000 mAh |
| Continuous current (high-drain cells) | 10–35 A | 30–45 A |
| Best-known drone cells | Molicel P28A (2800 mAh, 35 A), Sony/Murata VTC6, Samsung 30Q | Molicel P42A (4200 mAh, 45 A), Molicel P45B (4500 mAh, 45 A), Samsung 40T/50S |
The 21700 wins on every number except size and weight per cell, and even then it carries more energy per gram. The 18650 still makes sense where a pack has to be short or where the drone only ever draws a few amps — small fixed-wings, ground stations, and 4S packs for a 4″ long-range micro. 21700 Li-ion batteries · 18650 Li-ion batteries.
The Molicel numbers
Three Molicel cells cover almost every drone pack built today. P42A (21700, 4200 mAh, 45 A) is the workhorse: high current, moderate cost, the default for a 6S 7″ pack. P45B (21700, 4500 mAh, 45 A) is the newer cell with 7% more capacity and lower internal resistance — it sags less and runs cooler at the same current. P28A (18650, 2800 mAh, 35 A) is the high-drain 18650 for packs that must stay compact. All three are sold as bare cells for pack builders and assembled into packs in our Li-ion battery packs.
How a drone Li-ion pack is built
Cells go in series to raise the voltage (6S = six cells, 21.6 V nominal, 25.2 V full) and in parallel to raise capacity and current (2P = two cells side by side, doubling both). A 6S2P pack of P42A cells is twelve cells, 8400 mAh, 90 A continuous, about 850 g — the standard 7″ long-range pack. Compare a 6S 1550 mAh LiPo at 250 g for a 5″ quad and you see why the airframe has to be built for it.
- Cells are joined by spot-welded nickel strip, never soldered directly — the heat of soldering damages the cell’s internal seal. Pack builders use a spot welder and pure nickel (not nickel-plated steel).
- A balance lead is brought out from every series junction, exactly like a LiPo, so a normal balance charger keeps the cells matched. Drone packs use no BMS — it would limit current and add weight.
- Cells are matched by capacity and internal resistance before assembly so parallel groups share current evenly.
- The main lead is 10–12 AWG silicone wire to an XT60 or XT90, sized for the pack’s current.
- Fish paper and heat-shrink insulate the cell tops and wrap the pack; a strap slot or foam pad on the frame carries it.
Our own Li-ion packs are built exactly this way in Gurugram — Molicel P28A, P42A and P45B cells, spot-welded, balance-tapped, from 1S to 12S and 1P to 4P, with an XT-60 or XT90 connector of your choice. They are assembled to order and dispatched within 3–4 business days; browse them under Made in India Li-ion packs.
Flying and charging a Li-ion pack
- Set the charger to Li-ion, 4.20 V per cell (some cells accept 4.25 V; P42A/P45B are 4.20 V). Charge at 0.5–1C.
- Land at 3.0–3.2 V per cell — lower than a LiPo, because the Li-ion curve is flatter and usable further down. Set the OSD warning accordingly.
- Expect voltage sag on punch-outs. Fly it like a cruiser and it will reward you with 20–40 minute flights on a 7″.
- Storage is easier than LiPo — 3.6–3.7 V per cell, no puffing, and 300–500 cycles at moderate loads.
Cells and chargers: Li-ion cells · Chargers · The LiPo guide covers the rest of the battery vocabulary.