Roadster 18650 · Generation 1

Roadster ESS

6,831 commodity 18650 cells in eleven sheets. The pack that proved a lithium-ion sports car could work.

Undisclosed18650 cylindrical2008 – 2012Documented

Gross capacity: 53 kWh; conflicting reports
Usable capacity: Unknown
Cells: 6,831
Pack mass: 450 kg

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Pack · top view

11 modules

Cell supplier: Undisclosed; Reported: Sanyo or Panasonic
Cell: Roadster 18650 cell
Vehicles: Roadster
Built at: Hethel Menlo Park

The Roadster's Energy Storage System (ESS) was Tesla's first battery pack. Instead of waiting for purpose-built automotive cells, Tesla wired 6,831 commercially available 18650 cells, the same format used in laptops, into a single liquid-cooled enclosure behind the seats.

The cells were grouped into eleven sheets. Each sheet held nine series-connected bricks of 69 parallel cells, which gives the commonly cited 99s69p layout. Tesla's own documentation describes the pack as roughly 53 kWh at 375 volts, weighing about 450 kg.

Specifications

Pack data, value by value

Manufacturer-confirmed
Documented
Community-reported
Estimated

Every value shows its evidence level and sources. “Unknown” means no source we trust has published it. We never fill gaps with assumptions.

Gross capacity: 2 reported valuesspread 3 kWh · 5.5%

Filled dot: the value shown as primary (the most specific source for this pack). Rings: other reported values. Differences often come from different definitions of gross capacity.

Gross capacityTotal energy incl. bottom buffer: 53 kWhConfirmed[1]
Tesla described the pack as roughly 53 kWh.
Other reported values:
56 kWh[2]An earlier version of Tesla's document cited 56 kWh; forum discussion attributes the difference to the assumed nominal cell voltage.
Usable capacityEnergy available 100% → 0%: Unknown
Chemistry: Unknown
Laptop-class lithium-ion cells; cathode chemistry not published.
Cell format: 18650Confirmed[1]
Cell supplier: Disputed
Tesla did not publish the cell supplier.
Sources report different values. None is marked as correct:
Sanyo Electric[5]Forum reports describe Sanyo 2.2 Ah laptop cells.
Panasonic Energy[3]A spec aggregator lists Panasonic NCR18650A cells.
Cell count: 6,831Confirmed[1][3]
ConfigurationSeries × parallel: 99s69pCommunity[2]
99 × 69 = 6,831. Eleven sheets of nine series bricks.
Modules: 11Confirmed[1][3]
Tesla called them sheets.
Nominal voltage: 375 VConfirmed[1]
Architecture: Unknown
Pack mass: 450 kgDocumented[1][3]
About 450 kg (992 lb).
Energy densityPack level: 118 Wh/kgEstimated
Calculated by Tesla Battery Atlas from gross capacity ÷ pack mass. Not a published figure.
Structural pack: NoEstimated
No structural role documented.
Peak DC charging: Unknown

The cell

Roadster 18650 cell

A commodity 18650 cell of the kind used in laptops, chosen because it was readily available and affordable in 2008. Tesla described modifying the cells for automotive use.

Cell data

Dimensions: Ø18 × 65 mmConfirmed[1]
18650 = 18 mm diameter, 65 mm length.
Capacity: Disputed
Sources report different values. None is marked as correct:
2.2 Ah[5]
Nominal voltage: Unknown
Energy per cell: Unknown
Chemistry: Unknown
Commercially available laptop-class lithium-ion cells; the cathode chemistry was not published.

Capacity in context

Gross capacity of every documented pack. Hatched bars are disputed ranges; packs with unknown capacity are omitted.

Applications

Where this pack is installed

Each row is a documented link between this pack and a vehicle variant, with its factory, period and evidence. A variant may also appear with other packs.

Roadster (2008)Open in finder

Variant	Period	Factory	Market	Code	Evidence
RoadsterRoadster	2008 – 2012	Hethel, Menlo Park	Not market-specific	—	Documented[4][1] Gliders built by Lotus in Hethel; final assembly for North American cars in Menlo Park.

Performance

Charging, advantages and tradeoffs

Peak DC charging

Unknown

No verified charging curve for this pack is in the database yet. Curves vary with temperature, state of charge and software, so we only publish curves backed by repeatable measurements.

Advantages

Used cells that were already in high-volume production, which made the pack possible in 2008 without a custom cell program. [1]

Tradeoffs

Packs are hand-built in low volume, which keeps replacement and upgrade packs expensive. [7]

Identification

How to tell if your car has it

Every first-generation Roadster left the factory with this pack. A car may have since received the Roadster 3.0 (R80) upgrade pack, so check the service history.
The part number on the high-voltage battery label and Tesla service records are definitive. A VIN alone does not encode the cell supplier or pack code.

History

Lineage in the Roadster 18650 family

The original Roadster's energy storage system wired 6,831 commodity 18650 cells into eleven sheets. A hand-built upgrade pack followed in 2016.

Feb 2008Documented[4][1]
First Roadster delivered
Tesla's first production car carries 6,831 commodity 18650 cells in a 53 kWh pack.

Related packs

Model S 85 vsRoadster 3.0 (R80)vs

Sources

7 references

[1]
Tesla Roadster Battery System (Tesla Motors technical document, archived copy)
Tesla Motors via ScribdofficialConsulted 28 Oct 2026Pending direct review
Third-party archived copy of a Tesla document.
[2]
Roadster battery (ESS)
Tesla Motors ClubcommunityConsulted 28 Oct 2026Pending direct review
[3]
Tesla Roadster specifications comparison
EVSpecificationsdatabaseConsulted 28 Oct 2026Pending direct review
[4]
Tesla Roadster (first generation)
WikipediacommunityConsulted 28 Oct 2026Pending direct review
[5]
Tesla Roadster batteries
Tesla Motors ClubcommunityConsulted 28 Oct 2026Pending direct review
[6]
Tesla Roadster Mk1 (2008–2012) review
evopressConsulted 28 Oct 2026Pending direct review
[7]
Tesla Roadster 3.0 battery upgrade (R80)
ElectrekpressPublished 8 Jul 2016Consulted 28 Oct 2026Pending direct review