Second-Hand EV Batteries for Campervan Use: Complete Guide
Using a second-hand electric vehicle battery for your campervan is the ultimate DIY power move. You can get 7kWh of storage (equivalent to a 560Ah 12V battery bank) for £400–800 — a fraction of the cost of new LiFePO4 batteries.
I have seen several successful DIY EV battery conversions. I have also seen a few fires. This is not a project for beginners. It requires serious electrical knowledge, high-current DC experience, and comfort with the safety risks.
This guide covers the options, costs, and risks of using second-hand EV batteries in campervans.
Why Consider an EV Battery?
| Metric | New LiFePO4 (200Ah) | Nissan Leaf Module (7.4kWh) | Tesla Module (5.3kWh) |
|---|---|---|---|
| Capacity | 200Ah @ 12V (2.5kWh) | 7.4kWh @ 14V | 5.3kWh @ 24V |
| Cost | £500–600 | £200–300 | £300–500 |
| Cells | 4 × prismatic LiFePO4 | 2 × pouch LiFePO4 | Multiple 18650 cells |
| BMS included | Yes | No | No |
| Safe for vehicle use | Yes (designed for it) | Yes (designed for EV) | Yes (designed for EV) |
| Weight | 20kg | 28kg | 25kg |
| DIY difficulty | Low | High (DIY BMS required) | High (DIY BMS required) |
| Fire risk | Low | Low (but cells must be protected) | Moderate (18650 cells) |
Best Donor Batteries
Nissan Leaf (40kWh / 62kWh Pack)
The most popular donor for campervan builds. The pack contains 24 or 48 modules, each module being 7.4kWh at 14V (two cells in series). You can use one module (7.4kWh) or two in parallel (14.8kWh).
| Spec | Leaf Module (Gen 2, 2018+) |
|---|---|
| Chemistry | LiFePO4 (actually NMC — nickel manganese cobalt) |
| Voltage (nominal) | 14.0V (two cells × 7.0V each) |
| Voltage range | 12.0–16.8V |
| Capacity | 7.4kWh |
| Weight | 28kg |
| Dimensions | 300 × 220 × 120mm |
| Cost (used) | £200–350 |
Pros: High capacity, known voltage (14V works with a 12V system with a DC-DC converter), relatively safe chemistry
Cons: Heavy, NMC chemistry is more volatile than LiFePO4 if overcharged, needs a custom BMS
Tesla Model S (85kWh Pack — 22 Modules)
Each module is 5.3kWh at 24V (nominal). Used in many high-end DIY camper builds.
| Spec | Tesla Module (85kWh pack) |
|---|---|
| Chemistry | NCA (nickel cobalt aluminium) |
| Voltage (nominal) | 24.0V |
| Voltage range | 20.0–25.2V |
| Capacity | 5.3kWh |
| Weight | 25kg |
| Dimensions | 680 × 300 × 80mm |
| Cost (used) | £300–500 |
Pros: High power density, known reliability
Cons: 24V system needs a DC-DC converter (24V → 12V), NCA chemistry is volatile (more fire risk than LiFePO4), custom BMS needed
BMW i3 (22kWh / 33kWh Pack)
The i3 pack contains 8 modules, each 2.75kWh at 12V. Two modules in parallel = 5.5kWh.
| Spec | BMW i3 Module |
|---|---|
| Chemistry | NMC |
| Voltage (nominal) | 12.0V |
| Voltage range | 10.0–13.8V |
| Capacity | 2.75kWh |
| Weight | 12kg |
| Dimensions | 300 × 200 × 60mm |
| Cost (used) | £150–250 |
Pros: Compact, 12V compatible without converter, relatively safe
Cons: Lower capacity per module, needs custom BMS
System Design
12V System (Nissan Leaf Module)
Leaf Module (14.0V nominal)
│
├── BMS (DIY — monitoring + cell balancing)
│
├── DC-DC converter (14V → 12.8V, 30A+)
│
├── 50A fuse
│
└── Positive busbar → existing 12V system
The Leaf module's 14V nominal voltage is higher than a standard 12V system (13.2V for LiFePO4). You need a DC-DC converter to drop it to 12.8V for the van. A Victron Orion-Tr 12/12-30 (30A) works.
24V System (Tesla Module)
Tesla Module (24.0V nominal)
│
├── BMS (DIY)
│
├── DC-DC converter (24V → 12V, 40A+)
│
├── 60A fuse
│
├── 12V busbar → existing 12V system
│
└── 24V inverter (if using 240V from 24V)
A 24V system needs a 24V inverter (or a step-down converter to 12V). Victron makes 24V MultiPlus inverters. The advantage is lower current for the same power.
The BMS (Critical)
EV modules do NOT come with a BMS. You must add one.
| BMS Type | Cost | Works With | Difficulty |
|---|---|---|---|
| Daly Smart BMS | £50–150 | Leaf, Tesla, i3 | Moderate |
| JK BMS | £80–200 | Any lithium pack | Moderate |
| REC BMS | £200–400 | Professional | High |
| Arduino/ESP32 DIY BMS | £30–100 | Any | Very high |
For a Leaf module: A Daly 150A Smart BMS (with Bluetooth) works. Wire it to the two cell groups. The BMS handles over-voltage, under-voltage, over-current, and temperature protection.
Safety
This is the most important section. EV batteries store enormous amounts of energy. A 7.4kWh Leaf module stores 15× the energy of a 100Ah lead-acid battery. If it fails, it fails violently.
| Risk | Prevention |
|---|---|
| Over-charge (fire) | BMS with over-voltage protection. Never charge above 16.8V for Leaf, 25.2V for Tesla. |
| Over-discharge (cell damage) | BMS with under-voltage protection. Never discharge below 12.0V for Leaf, 20.0V for Tesla. |
| Physical damage (internal short) | Mount the module in a reinforced steel box. Protect from road debris. |
| Thermal runaway | Use a fire-resistant enclosure (steel or aluminium, not wood). Add a smoke alarm nearby. |
| Water ingress | IP65 enclosure. EV modules are not sealed for outdoor use. |
| High-voltage shock | Leaf modules are 14V (safe to touch). Tesla modules are 24V (still safe). The danger is the current (500A+ short circuit current). |
| Improper BMS configuration | Use a pre-configured BMS for your specific module. Do not guess parameters. |
Cost Comparison
| System | Capacity | Cost (Components) | Cost per kWh | DIY Difficulty |
|---|---|---|---|---|
| 200Ah LiFePO4 (new) | 2.5kWh | £500–600 | £200–240/kWh | Low |
| 2 × 200Ah LiFePO4 (new) | 5.0kWh | £1,000–1,200 | £200–240/kWh | Low |
| Leaf module (used) | 7.4kWh | £200–350 (module) + £80–200 (BMS) + £60–100 (DC-DC) = £340–650 | £46–88/kWh | High |
| Tesla module (used) | 5.3kWh | £300–500 (module) + £100–200 (BMS) + £80–150 (DC-DC) = £480–850 | £90–160/kWh | High |
| 2 × Leaf modules (parallel) | 14.8kWh | £600–1,200 | £40–81/kWh | Very high |
Is It Worth It?
| If You... | Recommendation |
|---|---|
| Are experienced with high-current DC systems | Worth considering — EV batteries are cost-effective |
| Are a first-time van builder | Buy new LiFePO4. The cost premium is worth the safety and simplicity. |
| Want the most capacity for the lowest cost | EV battery is the way to go. 14.8kWh for under £800. |
| Need a simple, plug-and-play system | Buy new LiFePO4. EV batteries are not plug-and-play. |
| Do not want to learn about BMS configuration | Buy new LiFePO4 with a built-in BMS. |
FAQ
Q: Is it legal to use an EV battery in a campervan? A: Yes. There is no law against using second-hand EV batteries in a vehicle. Insurance may ask about the electrical system — disclose the modification.
Q: How long does a used EV battery last in a campervan? A: An EV battery at end-of-vehicle-life typically has 70–80% of original capacity remaining. In campervan use (gentler cycling than EV use), it can last 5–10+ more years. Total lifespan from manufacture: 15–20 years.
Q: Can I connect an EV battery directly to my van's 12V system? A: No. The voltage is different (14V Leaf, 24V Tesla) and you need a DC-DC converter to regulate it to 12.8V. Direct connection damages 12V equipment.
Q: Do EV batteries need ventilation? A: Yes. NMC and NCA cells produce flammable gas if overcharged. The enclosure should have a vent to outside air.
Q: Can I charge an EV battery with solar panels? A: Yes, through an MPPT charge controller. Configure the controller for the battery's voltage and absorption parameters. The MPPT charges the battery, the BMS protects it.
