Why people consider them
Used EV batteries can offer 20, 40 or even 80 kWh of storage for a surprisingly low purchase price. They also arrive with useful automotive engineering: a strong enclosure, cell monitoring and, in many packs, contactors, current sensing and temperature sensors. Reusing that hardware can save money and avoid rebuilding parts the vehicle manufacturer already designed well.
The real job is finding out what capacity remains, then choosing a controller and inverter combination that is known to work with that exact pack. A low battery purchase price can still become a very low complete-system price; it should be calculated, not dismissed.
The three costs that matter
Worked estimate A nominal 40 kWh pack at 82% measured SOH, operated through an 80% SOC window, offers an estimated 26.24 kWh DC-usable before inverter losses: 40 × 0.82 × 0.80. At an illustrative £2,000 pack price, battery-only cost is £50/nominal kWh and about £76/usable kWh. If transport, testing, controls, protection, enclosure, inverter and competent installation make the complete project £8,500, the figure becomes about £324/usable kWh. These are arithmetic assumptions—not a live UK quotation.
UK salvage listings are volatile, often omit verified capacity and may carry transport restrictions. No defensible comparable live-price dataset was found for this review, so the structured price table is intentionally empty rather than presenting seller claims as evidence.
Why “40 kWh” is not 40 usable kWh
Original capacity may be gross or usable. Ageing reduces capacity and power; imbalance means the weakest cell group can limit the pack. Temperature, the retained BMS limits, a deliberately narrower stationary SOC window and conversion losses reduce delivered energy further. Capacity SOH alone does not reveal internal resistance, isolation condition or damage history.
Chemistry changes the design, not the need for protection
| Family | Stationary implications | Caution |
|---|---|---|
| NMC | High energy density; widespread in European EV packs | Variant-specific voltage/thermal limits; ageing and cooling history matter |
| NCA | High specific energy and power | Requires disciplined monitoring and thermal management |
| LFP | Lower energy density, long cycle-life potential and flatter voltage curve | Flat curve makes voltage-only SOC estimation difficult; “safer” never means hazard-free |
Cell chemistry does not establish pack suitability. Mechanical damage, contamination, isolation, sensing, contactors, software limits and enclosure design remain decisive.
How the battery and inverter talk
In the car, several computers exchange messages with the battery over CAN. Those messages include state of charge, temperature, faults and the power the pack can safely accept or deliver. Remove the car and the battery may wait for messages that are no longer present.
Translates CAN dataPack contactors
Connect when readyCompatible HV inverterHome energy system
A battery emulator or controller reproduces the necessary conversation and translates the battery limits into a protocol the inverter understands. This is why matching voltage alone is not enough. Battery-Emulator documents selected Nissan Leaf, Tesla, BMW, MEB, Renault and Hyundai/Kia integrations, but each battery, inverter, hardware and software combination still needs checking against the current project documentation.
High-voltage boundary: An EV pack can retain lethal voltage after the vehicle is isolated. Opening packs, bypassing interlocks or doing live HV work needs appropriate equipment, knowledge and procedures; this site does not provide those instructions.
What “supported” really means
Battery-Emulator is a translation layer, not a universal battery adapter. Its current documentation separates inverter integrations into three practical levels: well supported with multiple reported installations, working with limitations, and compatible but difficult to set up. It also marks testing-only and unsupported entries. Treat that rating as project evidence, not approval from the battery or inverter manufacturer.
| Inverter family | Project status | Planning point from the project |
|---|---|---|
| Deye / Sunsynk HV | Well supported | Selected three-phase HV models; external pre-charge is listed as required. |
| Fronius GEN24 Plus | Well supported | Single- and three-phase models; documented voltage windows and built-in pre-charge. |
| GoodWe ET / BT / EH / BH | Well supported | Hybrid and AC-coupled families are documented separately. |
| Solis | Well supported | Protocol support covers various models, but their battery-voltage windows differ. |
| FoxESS H1 / H3 / AC1 / KH | Works with limitations | Needs a CAN channel separate from the EV battery bus. |
| SolaX X1 / X3 | Works with limitations | Also needs a separate CAN channel; model voltage ranges differ. |
| Sungrow SH families | Works with limitations | Protocol and regional-model details vary. |
| Huawei SUN2000 | Not supported | The project says a DC/DC converter would be required. |
The list changes as the project develops. Before choosing hardware, check the live supported-inverter table and the detailed page for that exact model.
Five checks for every combination
- Battery support: the exact vehicle generation or BMS appears in the current documentation.
- Inverter support: the exact inverter family and protocol are documented, not merely a similar brand name.
- Voltage window: the pack’s full operating range fits inside the inverter battery-input range.
- Pre-charge and contactors: establish whether these are retained in the pack, built into the inverter or controlled externally.
- CAN architecture: some inverters tolerate a shared bus; others require an isolated second CAN channel.
Project software can expose voltage, current, state of charge, temperature, cell-voltage spread, remaining capacity, faults and insulation data where the battery integration provides them. A missing value is not the same as a healthy zero reading.
Pack families in the current project
The live catalogue is much broader than the first version of this site suggested. It includes documented integrations for Nissan Leaf/e-NV200, BMW i3, Tesla S/X and 3/Y, Renault Zoe, VW-group MEB, Hyundai/Kia 64 kWh and E-GMP families, BYD vehicle packs, several MG and Stellantis platforms, selected plug-in hybrid packs and third-party BMS units. “Listed” still does not mean every year and variant behaves identically. Start with the project’s current battery list, then read the page for the exact pack.
The site’s machine-readable family dataset remains a conservative overview. The first detailed family is the Nissan Leaf; more individual pages will only be added where project documentation and manufacturer evidence can be combined into something genuinely useful.
Build the cost from what this pack needs
- battery purchase and transport;
- health or capacity checks where the available evidence is weak;
- controller or emulator and its supported hardware;
- a compatible inverter;
- protection, cabling and any containment not retained from the vehicle;
- cooling only where the pack and intended duty require it;
- electrical installation and grid-connection work.
Do not add contactors, current sensors or cooling hardware automatically if the complete pack already contains serviceable equipment that the supported integration uses. Put the actual items into the battery cost comparison.
Test the household case first.
Model energy flows and tariff value before choosing a battery architecture.
Sources and evidence limits
- Nissan Technical Review 82 for the 40 kWh Leaf battery development.
- Battery-Emulator for documented open-source integration scope (project evidence, not OEM approval).
- Energies review of second-life stationary batteries for SOH, screening and integration challenges.
- ENA energy-storage connection guidance.