Why Second-Life Tesla Modules Might Be the Best Battery for Your EV Build

You’re knee-deep in the planning phase of your EV conversion. You’ve picked your donor car, mapped out your drivetrain game plan, maybe even chosen your motor. But when it comes to the battery—arguably the heart of your build—you’ve hit the wall. Everyone’s throwing around chemistry acronyms and voltages like it’s a secret club. And then someone mentions second-life Tesla modules. Cheap, high-performance, already proven in the wild.

But here’s the real question: are they legit for your build? The short answer—yes, and then some. Let’s break down why.

First: What Are Second-Life Tesla Modules?

Second-life Tesla modules are exactly what they sound like—battery packs harvested from used or salvaged Teslas, most commonly the Model S and Model X. These aren’t junkyard scraps. They’re lithium-ion modules that still carry anywhere from 85% to 99% of their original capacity. When Tesla decommissions a vehicle (say, after a crash), the battery is often still very usable. Companies scoop up these packs, test them and sometimes replace a default cell, and resell them to EV builders at a serious discount and with a month warranty.

And they’re not some fringe option. According to Recurrent Auto, Tesla batteries can retain 80–90% of their original range even after 150,000+ miles. That makes them one of the most reliable lithium battery sources for second-life use on the market today.

Why They Work So Well for Conversions

Let’s cut to it: you’re here because you want the most bang for your volt. Second-life Tesla modules offer a killer combo:

1. Energy Density That Actually Moves You

Each Tesla Model S/X module (from 2012–2016) packs about 5.3 kWh. Stack 5–6 of them together and you’ve got a 26–32 kWh pack—enough for ~100–140 miles of range depending on your motor and weight setup. That’s plenty for most classic conversions, weekend cruisers, or daily drivers with moderate commutes.

2. High Discharge = Performance Potential

Tesla modules can push out serious amps. They were designed for 4,600 lb performance sedans—so giving your 3,000 lb VW Beetle or Mazda RX-7 a jolt is child’s play. You’ll get up to 1,000A peak discharge depending on your BMS and configuration. That translates to real acceleration and highway-ready behavior.

3. Smart Engineering, Already Done

Each module comes with an integrated liquid cooling system, using cleverly designed coolant tubes that run between the cells themselves—not separate plates. The coolant flows directly through the module via clearly marked IN and OUT ports, making it easy to hook up your preferred loop. This design eliminates the need for external cooling plates or complex add-ons. It’s all built-in, smartly engineered, and thermally efficient, thanks to Tesla’s scale-tested architecture—used in hundreds of thousands of vehicles.

Instead of designing a custom cooling system or guessing at thermal distribution, you’re working with a setup that’s already proven to handle high loads, fast charging, and long road cycles without breaking a sweat.

Price: The Real-World Budget Advantage

Here’s the kicker—you’ll likely pay about $100–$150 per usable kWh for second-life Tesla modules, depending on condition and supplier. Compare that to $300+/kWh for brand-new NMC or LFP packs, and you’re easily saving thousands.

Let’s say you want a 30 kWh pack:

1. New: ~$9,000+

2. Second-life Tesla: ~$3,000–$4,500

That’s real savings—especially when you’re also budgeting for controllers, mounts, DC-DC converters, and wiring.

Downsides? Sure—But They’re Manageable

Let’s be real. No solution is perfect. Here’s what to consider:

Voltage Management: Tesla modules have a nominal voltage of ~22.8V per module. You’ll need to design your system around that—either wiring them in series to hit your desired pack voltage (e.g., 5 modules = ~114V nominal) or using a compatible motor/inverter that can handle Tesla voltages.

Cooling Requirements: These modules need thermal management. You can’t just toss them in a box and hope for the best. Luckily, the built-in cooling plates make it easy to set up a basic closed-loop liquid cooling system (using off-the-shelf pumps and radiators).

BMS Compatibility: Off-the-shelf battery management systems like Orion BMS, Dilithium, and Thunderstruck are all compatible with Tesla modules, though they typically require some wiring, programming, and patience to get set up. Expect a learning curve—but you’ll also find strong community support. These modules are popular, and there are plenty of step-by-step guides in open-source forums to walk you through it.

One notable alternative is the Vero BMS V2. It’s specifically designed for Tesla modules and eliminates the need to replace the tap boards, making installation faster and far less invasive. If you’re looking to streamline your setup without compromising on performance, it’s a solid, EV-focused solution worth considering.

Who Should Not Use Tesla Modules?

If you're building a lightweight electric motorcycle, a solar-powered camper van, or a marine/off-grid application, Tesla modules might be overkill. In those cases, safer, simpler packs like LiFePO4 are often a better fit due to lower energy density and more forgiving charge/discharge profiles.

But for traditional EV conversions (especially cars and light trucks), Tesla modules are a sweet spot of power, price, and scalability.

Real-World Builds Using Tesla Modules

Still on the fence? Here are a few real-world examples:

Take the Karmann Elektra by Flashdrive Motors, a fully electric 1969 Volkswagen Karmann Ghia that blends vintage character with second-life Tesla performance. Powered by reclaimed Model S modules, the build delivers real-world range, seamless throttle response, and a power curve that feels nothing like a typical retro ride. Shops like Flashdrive are setting the new bar—combining proven Tesla hardware with clean design and practical integration. This isn’t just about going electric; it’s about making something smarter, faster, and still true to the original soul.

DIYers on forums like DIY Electric Car and the EV Conversion Facebook group have documented hundreds of builds using Tesla modules, from VW Buses to muscle cars to quirky urban commuters.

This isn't theoretical—it’s already the go-to move for a reason.

Quick Note

Make sure you’re getting tested modules with verified remaining capacity—State of Health (SOH) should be clearly disclosed. Sellers should also provide proof of balancing and internal resistance checks. This isn’t just a best practice—it’s essential. Without it, you’re rolling the dice on safety, performance, and longevity. Steer clear of any listing (especially on platforms like eBay) that can’t provide this data.

And just as critical: look for a minimum 6-month warranty. That window gives you time to fully cycle the pack, balance it under real-world loads, and identify any hidden issues before they become expensive problems. If a seller isn’t confident enough to offer that, it’s a red flag.

Final Word: A Smart Shortcut That Doesn’t Cut Corners

In the chaotic, trial-and-error world of EV conversions, second-life Tesla modules offer something rare: a shortcut that still delivers performance and reliability.

They’re not perfect—but they are proven, affordable, and powerful. And unlike building a custom pack from raw cells, they don’t require a chemistry degree or a month of spot welding. You’ll spend less time obsessing over spreadsheets and more time actually getting your build on the road.

So if you’re staring down your battery options and want to balance performance, budget, and peace of mind—second-life Tesla modules might just be your best bet.