Home › Batteries › BMW i3

BMW i3 Battery for Home Energy Storage

The BMW i3 high-voltage pack is a well-documented second-life candidate: the SME BMS remains functional outside the vehicle, there is no VIN pairing on the pack CAN interface, and the pack is liquid-conditioned: liquid-cooled, individually monitored at cell-group level, and available in three capacities (60 Ah / 94 Ah / 120 Ah).

Can a BMW i3 battery be used for home storage?

Yes. The i3 pack is well suited to second-life use for three specific reasons for three reasons. First, BMW's SME (Sensor Modul Elektronik) BMS remains fully functional when the pack is removed from the car — no immobiliser lock-out and no VIN check on the pack CAN interface. Second, the pack has a liquid-cooling loop integrated with the vehicle HVAC system; when reused, this loop is either terminated in a small stationary chiller or left passive (the pack tolerates passive operation at moderate charge rates). Third, i3 cells (Samsung SDI prismatic, 60 Ah / 94 Ah / 120 Ah) show consistent degradation characteristics and typically retain 85–92 % SoH after 100 000 km of vehicle use.

Second-life is explicitly permitted under EU Regulation 2023/1542 (Batteries Regulation), Article 59. The pack, however, remains a high-voltage assembly and must be installed by a qualified electrician.

Battery generations and capacity

Two energy figures, one pack. Gross is the nameplate energy of the cells; usable is what the BMS will cycle. BMW marketing rounds the gross figures to 22 / 33 / 42 kWh, and mixing a rounded gross figure for one generation with a usable figure for another is a common source of error in second-life listings. For sizing a stationary system, use the usable column: 18.8 / 27.2 / 37.9 kWh. Sources: BMW technical data (60 Ah, 94 Ah), BMW specifications (120 Ah), and BMW’s 94 Ah announcement, which states the 60 Ah pack as “22 kWh (gross)/19 kWh (net)”.

On cell designations. BMW and Samsung SDI identify these cells by capacity and by BMW part number, not by a generation letter. The 94 Ah cell is named Samsung SDI AIO 5.5 in the peer-reviewed literature (Gailani et al., IEEE 2020, which measured it at 173.2 × 45.2 × 175.8 mm, 2.7–4.15 V); the 120 Ah cell is a VDA BEV2 format cell. Beware of “E3” as a cell name in second-hand listings: Samsung SDI does sell an E3 cell, but it is a 111 Ah cell for stationary grid storage and is not the i3 cell. Cathode designations (NMC 111, NCM 622) come from third-party teardowns, not from BMW, which states only “lithium-ion”.

All three generations share the same mechanical envelope, the same 96s configuration, and the same SME BMS hardware — only the cell chemistry and internal firmware calibration differ. From the BMS-EV controller's perspective, the CAN message set is identical across generations; firmware auto-detects the pack variant from the SME's identifier frame during handshake.

Technical specifications

Original BMW BMS is retained

Do not disassemble the pack. The SME master board and its eight slave boards continue to perform cell balancing, over-voltage / under-voltage cutoff, over-temperature cutoff, isolation monitoring, and contactor sequencing. The BMS-EV controller does not replace these functions; it reads their reported state and re-transmits it in the format the hybrid inverter expects (Pylontech, BYD, or Deye native — see below).

Cell balancing on the SME is passive, resistor-based, and operates during charging above 3.9 V/cell. In stationary use, plan for regular top-of-charge cycles (approximately once per week charging to 95 %+) so the balancer has an opportunity to act. Storage held permanently at 60 % SoC without top balancing will accumulate imbalance over months.

CAN + LIN wake protocol

Unlike a Tesla or Nissan pack — which can be woken by simply energising the 12 V auxiliary rail and toggling a wake-up pin — the BMW SME requires a valid LIN bus wake sequence before it will respond on CAN. The BMS-EV controller emulates the vehicle's Body Domain Controller (BDC): it sends a LIN break-and-sync followed by the SME wake frame, waits ~150 ms for the SME to boot its CAN transceiver, then begins CAN communication.

Without the LIN sequence the pack will remain in deep sleep and no CAN traffic will be observed. This is the single most common integration failure for DIY builds using generic Pylontech-emulator devices — they cannot wake an i3 pack. BMS-EV controllers shipped for i3 always include the LIN wake logic in firmware.

Contactors, precharge, HVIL and isolation

The i3 pack contains two main contactors (positive and negative) plus an internal precharge circuit (relay + 40 Ω resistor). Sequencing is: (1) HVIL loop confirmed closed, (2) negative contactor closes, (3) precharge relay closes for 300–500 ms to charge the inverter's DC-link capacitors through the resistor, (4) positive contactor closes, (5) precharge relay opens. The BMS-EV controller commands this sequence via CAN — no external contactor wiring is required.

HVIL (High Voltage Interlock Loop) is a low-current safety circuit that runs through the pack lid, the service disconnect, and (in the vehicle) all HV connectors. Any break opens the contactors within milliseconds. In stationary use the loop is closed with a short jumper on the pack connector — a service disconnect (pilot switch) is strongly recommended between the pack and the DC bus so the loop can be opened deliberately during maintenance.

Isolation monitoring runs continuously. If pack-to-chassis resistance falls below approximately 100 Ω/V (i.e. ~40 kΩ at 400 V), the SME opens contactors and reports the fault on CAN.

Compatible hybrid inverters

Any inverter with a DC battery input covering the 260–395 V range and a CAN protocol supported by the BMS-EV controller is compatible.

Known limitations

• LIN wake is mandatory. Any controller or emulator that speaks only CAN will fail to bring the pack out of sleep. Verify LIN support before purchase.
• Avoid parking the pack at a high state of charge. This is general lithium-ion behaviour, not an i3-specific figure. In the most finely resolved calendar-ageing study available, capacity fade rises in a marked step at roughly 60 % SoC for NMC and NCA cells, with the sharpest effect at 100 %; the authors conclude that “high storage SoCs corresponding to low anode potential should be avoided” — and attribute the fade mainly to the graphite anode, which is largely independent of cathode chemistry (Keil et al., J. Electrochem. Soc. 163(9), 2016; that study tested 18650 cells, not i3 prismatic cells). A charge ceiling around 90 % is a pragmatic operating margin for a repurposed pack running outside BMW’s own BMS strategy, not a threshold taken from the literature. Two things we cannot tell you: there is no published data comparing high-SoC sensitivity between the 60 Ah, 94 Ah and 120 Ah cells, so no generation-specific limit can be stated; and BMW’s own vehicle guidance points the other way — Service Information SI B61 09 14 instructs that an i3 stored out of Transport Mode “should be charged to 100% prior to storage”, relying on the pack’s built-in buffer.
• Refrigerant loop is orphaned in stationary use. The pack tolerates ambient operation up to ~35 °C without cooling if peak C-rate stays below 0.3 C. Above that, add a small chiller loop (2–4 kW cooling capacity is sufficient) or de-rate the inverter.
• Service disconnect must be added externally. The vehicle service plug is an integral part of the HVIL; use a rated DC disconnect between pack and inverter for maintenance access.
• REX packs are supported but have different geometry. The range-extender i3 uses the same electrical pack — firmware makes no distinction.

Installation example — 42 kWh + Deye 10 kW

A typical mid-2020s residential installation:

• Solar array: 12 kWp (30 × 400 W panels)
• Inverter: Deye SUN-10K-SG04LP3-EU (three-phase, 10 kW AC, 160–700 V (5-25 kW) / 160–800 V (29.9-50 kW) DC battery port)
• Battery: BMW i3 120 Ah / 42 kWh, ~37.9 kWh usable
• Controller: BMS-EV BMW-i3 v3, pre-flashed for Deye HP3 protocol
• DC disconnect: 500 V / 32 A rated, pilot-switch type (for HVIL)
• Fuse: 200 A HRC gPV between pack and inverter

Typical daily behaviour for a Central European household (12 kWh/day consumption): fully covered from March to October; from November to February the pack supplies overnight and evening peaks, grid supplements during longest dark spells. Yearly grid import for a household previously drawing 4 500 kWh/year drops to approximately 600–900 kWh.

Frequently asked questions