Magnus (Estes Energy) Pack Benchmark

“What are the benefits of a Magnesium battery pack enclosure?” arrived in my inbox with a link to the Estes Energy website.

That got me looking at this particular design as a benchmark and also more generally about the use of magnesium as a structural material within the pack design.

This post has been built based on the support of and sponsorship from: illumion, Custom Power, Quarto Technical Services, Eatron Technologies and About:Energy

Company & Manufacturing Status

Estes Energy Solutions is San Francisco-based, founded April 2024 by engineers from Tesla, Sila, and Cummins (CEO Dustin Grace), and raised an $11M seed round in July 2025 co-led by BMW i Ventures and Fortescue. Target segments are mass-constrained applications: rail, marine, aviation, off-highway, and Class 8 trucking. Estes states it made its first commercial shipment of Magnus on 21 July 2026 under signed contracts, though no OEM customers are named. A US giga-thixomolding press is planned at roughly 30kg per shot, one shot per minute, targeted for the first half of 2027; thixomolding has historically been limited to parts under about 5kg, and while Chinese programmes are already moving larger applications into mass production, a press at this scale for a magnesium battery structure would still be a genuine step up, not an incremental one.

Platform Specifications

Estes publishes three product lines (LV, Magnus, Magnus+), each available in up to three sizes (I, II, III) built by adding parallel strings of the same pack.

	Magnus LV	Magnus	Magnus+
Application	Low-voltage / auxiliary	On-highway, commercial, marine	On-highway, commercial, marine
Dimensions (mm)	305 x 590 x 236	1332 x 590 x 236	1480 x 590 x 236
Mass (kg)	48	307	345
Voltage class 1 (min/nom/max)	48V (30/45/50)	400V (240/350/400)	500V (240/350/450)
Voltage class 2 (min/nom/max)	100V (60/90/100)	800V (480/700/800)	1000V (540/790/910)
Rated energy (kWh)	8.6	69.0	77.6
Gravimetric energy density (Wh/kg)	180	225	225
Volumetric energy density (Wh/L)	207	372	376

Common across platform: NCMA chemistry (as stated); cylindrical format visually consistent with 21700 (not textually confirmed); PPR/ECE R100.3; ISO 26262 to ASIL-D; ISO 21434; SAE J1939; 3,000+ cycles; WEG 50/50 thermal fluid; 80% charge recovery under 45 minutes.

Benchmark Summary

Magnus’s claimed 225 Wh/kg and 372 Wh/L (69kWh size) would lead every 21700-cell pack in the BatteryDesign.net database (1,971 packs), including the only other magnesium-enclosure 21700 pack on record, Stark Future’s VARG MX motorbike (202 Wh/kg), and sits roughly 32% above the closest scale/chemistry match, Tesla’s Model 3 pack (171 Wh/kg, aluminium, NCA). The database entries are built from teardowns, EPA filings, and datasheets; the Magnus entries are Estes’ own published figures, not yet independently verified at pack level.

Methodology Notes

Comparison data: BatteryDesign.net Pack Benchmark Database v1.7.07 (Brookvale Solutions Ltd), 1,971 packs, compiled from teardowns, EPA filings, and datasheets. Magnus data: Estes’ Spec Sheet (Rev. 2026.05), technology page, and June 2026 whitepaper.

Cell specification is not disclosed by Estes beyond “NCMA” chemistry. Two figures are derivable from Estes’ own numbers: combining the stated 82% cell-to-pack efficiency with the 69kWh/307kg pack figures implies a required cell-level specific energy of 274 Wh/kg, and the 400V/800V voltage classes imply series counts of ~96s/~192s at a standard ~3.65V/cell, consistent with the stated current ratings (300A / 197Ah implied capacity = 1.52C, matching the stated 1.5C continuous rating). Checked against LG Energy Solution’s current 21700 lineup, the closest match is the LG M58T (2022, 273 Wh/kg, 0.4% below the requirement) rather than the more commonly assumed M50 (267 Wh/kg, and confirmed NMC811+Si, not NCMA). Cell count is therefore best expressed as a range, ~3,400 to 3,900 cells, not a single figure.

No pack-level (69kWh) safety validation is published; Estes [1] cited thermal propagation test is run on the 9kWh LV pack.
No dielectric withstand or breakdown-voltage figure is published for the HV coating, only a system-level “works up to 1500VDC” claim.
Corrosion (ASTM B117) and flammability (FAA Ch.25) claims cite recognised test methods, but certificates are described as confidential / available on request.

Pack Mass vs Total Energy

Every mobility-application pack in the database with both mass and energy reported (n=839; stationary storage excluded). Diagonal lines mark constant gravimetric density; all four Magnus configurations are overlaid in red.

All four Magnus points sit above the bulk of the database cloud relative to the density guide lines, consistent with Estes [1] density claim, but none of the four have an independently verified mass or energy figure behind them.

21700-Format Packs: Gravimetric Energy Density

*Figure 2. 21700-format packs only (n=34). Blue = aluminium/other. Green = Stark Future VARG (magnesium). Red = Magnus.*

Magnus’s claimed 225 Wh/kg would top this list over the current leader, Stark Future’s magnesium VARG pack (202 Wh/kg), the only other magnesium 21700 pack in the database, and an independent data point corroborating the mechanism, though at a very different scale (6.5kWh motorbike vs. 69kWh commercial pack).

Key Comparators

Pack	Energy (kWh)	Mass (kg)	Wh/kg	Wh/L	Cells	Enclosure
Magnus I (Estes)	69.0	307	225	372	~3,400–3,900 (est.)	Magnesium
Stark VARG MX (best in DB)	6.5	32	202	N/A	400	Magnesium
Rivian R1T Gen2	149.6	787	190	266	7,776	Aluminium
Canoo LDV 190	78.8	430	183	293	4,416	N/A (reported Al)
Tesla Model 3 (2021)	82.0	480	171	205	4,416	Aluminium
Kreisel KBP63	63.0	393	160	203	N/A	N/A
21700 cohort average	N/A	N/A	166	181	N/A	mostly Al

Claimed Weight Benefit by Application

Estes’ whitepaper publishes mass savings across seven segments, comparing Magnus (225 Wh/kg) against a stated “170 Wh/kg commercial baseline.” Separately, in a July 2026 interview Estes described conventional commercial packs as sitting “around 170–190 Wh/kg at system level,” a range that brackets the single 170 Wh/kg figure used in the table below rather than independently corroborating it; both numbers still trace back to Estes itself, not a third-party baseline.

Application	Pack Energy (kWh)	Baseline Mass (kg)	Magnus Mass (kg)	Mass Saved (kg)	Reduction
Passenger Automotive (BEV)	80	470	355	115	24.5%
Defense / Autonomous (UGV)	100	590	440	150	25.4%
Aerospace (eVTOL)	150	1,765	1,333	432	24.5%
Marine (BEV vessel)	200	1,180	890	290	24.6%
Heavy Commercial (bus/delivery)	500	2,940	2,220	720	24.5%
Class 8 Truck (long-haul)	850	5,000	3,780	1,220	24.4%
Light Passenger Rail	3,500	20,600	15,600	5,000	24.3%

One ratio, seven segments Every row reduces to almost exactly the same 24.4% cut (24.3–25.4%), precisely 1 minus (170/225). It’s one headline ratio applied to seven baseline masses, not seven independently engineered comparisons; nothing indicates the 225 Wh/kg figure was re-derived per segment.

Certifications & Regulatory Claims

Magnus claims PPR/ECE R100.3, ISO 26262 (ASIL-D), ISO 21434, and SAE J1939, none with a certificate number, test lab, or completion date. UN38.3’s absence is worth noting since it’s the most commonly disclosed cert database-wide and close to baseline for any commercially transported lithium pack; it may simply be omitted from the one-page spec sheet.