The 2025 Nio Firefly battery uses LFP cells from Sunwoda and was originally suggested it would be to the CATL Choco-SEB swappable standard. However, see comment at end, this ended up being designed to be supported by the 5th gen Nio swap stations.
Metrics
- Gravimetric Density
- Energy = 134 Wh/kg
- Power = 372 W10s/kg
- Charge = 318 Wcont/kg
Specifications
- Usable Energy = 41.2 kW (total = 42.1 kWh)
- SoC Window = 97.9%
- Nominal Voltage = 358.4 V
- Nominal Capacity = 117.5 Ah
- Peak Power ~ 116 kW10s
- Pack Mass = 314 kg
- Configuration = 1 # packs
- 112 s 1 p
- Total # cells = 112
How many people with fast charge this pack when it can be swapped or easily charged overnight at home?
Charging
- Peak charge power = 100 kW
- Charge time (10 to 80% = 28 minutes
The battery pack looks very standard.
This post has been built based on the support of and sponsorship from: Quarto Technical Services, Eatron Technologies and About:Energy
Cell
Cell is made by Sunwoda and this is the first time Nio have used there cells in a product.
- Chemistry = LFP
- Format = Prismatic
- Capacity = 117.5 Ah
- Nominal voltage = 3.2 V
- Nominal energy = 375.9 Wh
Update, 23 October 2026: the 60 kWh option
Firefly launched a larger pack for the same car on 23 October 2026, so the 42.1 kWh LFP pack above is now the smaller of two options [3]. The new one uses ternary (NMC-type) lithium cells, which Firefly states, and is rated at 60 kWh and 560 km CLTC, up from 420 km [3]. Firefly’s brand marketing head had already named CATL as the supplier at a user event before the launch [4], and a pre-launch report said the same [5]. The launch coverage we found does not name a supplier, so we treat CATL as a claim made before launch and not yet repeated at it.
What a chemistry swap in the same envelope means
The reporting says the housing dimensions, mounting points and locking mechanism are the same for both packs, and that existing cars are upgraded by battery swap [3]. That is a sensible way to build a swappable range: the vehicle and the station only see the envelope, so the cells inside can change. Our arithmetic from the headline numbers is below. None of it is a published specification, and the reports give no pack mass or volume.
| Item | 42.1 kWh (LFP) | 60 kWh (ternary) | Note |
|---|---|---|---|
| Energy (kWh) | 42.1 | 60 | Our arithmetic: +43% in the same envelope |
| Range, CLTC (km) | 420 | 560 | +33% [3] |
| CLTC km per kWh | 10.0 | 9.3 | Our arithmetic; the gap may come from the usable window or rounding |
| Upgrade price, outright owners (CNY) | n/a | 17,000 | About 950 CNY per extra kWh (our arithmetic, 17.9 kWh) [3] |
| Battery rental, BaaS (CNY per month) | 399 | 599 | Upgrade service fee 3,000 CNY [3] |
Two things stand out. First, 43% more energy in an unchanged envelope is a volumetric energy density step of the same size, and that is the real benefit of moving from LFP to ternary cells for a pack whose box cannot grow. Second, the range grows by less than the energy does, so the 60 kWh option is not a free lunch on efficiency or usable energy, though the reports do not say why. We read the outright upgrade price as a fairly cheap way to buy 17.9 kWh, but it is Firefly’s price to its own customers and says little about cell cost.
The swap compatibility claim is the part that matters for design. A pack that can take either chemistry has to present the same electrical interface to the car, and it has to have a BMS able to handle both the LFP and ternary voltage windows and sensing. We could not find how Firefly handles that. See our Designing Swappable Batteries post for the general constraints.
References
- Firefly, Nio Firefly
- NIO and CATL Form Strategic Partnership on Battery Swapping, Nio Newsroom
- Nio Firefly launches larger 60-kWh battery pack, extending range to 560 km, CnEVPost, 23 October 2026
- Nio to launch larger 60-kWh battery pack for Firefly on October 23, CnEVPost, 16 October 2026
- Nio Firefly upgrades lineup with new 60kWh battery model launching October 23, report says, CarNewsChina, 19 October 2026
See also: Benchmarking Battery Packs, Choco-SEB, Sunwoda
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Yup, this is not the Choco-SEB compatible pack. Firefly is in a messy situation where it was originally going to have dedicated compact swap stations, but they decided last minute to integrate the brand’s packs into Nio’s 5th gen swap stations instead; they even showcased a working model shortly before the switch. I believe they said it was because they underestimated the bureaucracy and build time of swap stations in Europe compared to their experience in China, likely making the dedicated station’s size advantage for more quick and flexible installation irrelevant. The gen 5 Nio stations are only supposed to start appearing in August ’25 at the soonest.
Later, they announced the brand’s cooperation with the Choco-SEB standard, but that will only be for following models starting next year at the earliest; the current model won’t be compatible.
thank you for this insight, we have updated the post