Latest / Hardware Startups with Fexingo: Devices, Robotics, and Manufacturing Tech Companies / Why Hardware Startups Are Choosing Modular Batteries
Transcript
- Lucas: So, I was looking at teardown reports for a few popular e-bikes and power tools, and one thing kept jumping out: more and more of them are built around modular battery packs. Not glued-in pouches, but swappable, standardized cells you can actually buy. Luna: You mean like the old drill battery approach? Where you can pop one out and put another in? Lucas: Exactly. And it's not just drills anymore. We're seeing it in e-bikes, scooters, even some robotics platforms. The question is why now, and what are startups giving up when they choose modular over a fully integrated pack. Luna: Let's start with the obvious: what's the actual difference in design? Is it just about how the cells are arranged? Lucas: The core difference is architecture. An integrated pack is custom-designed for one product — cells are welded or glued into a rigid frame, often with a custom shape to fit that device. Modular means you're designing around standard cell formats, usually 18650 or 21700 cylindrical cells, and you're building a tray or a sled that lets the user swap them out or a tech replace them without destroying the product. Luna: So one is like a bespoke suit, the other is off-the-rack. But off-the-rack doesn't fit as well, right? What's the tradeoff? Lucas: The biggest tradeoff is energy density. When you pack cells tightly in a custom shape, you can squeeze more capacity into the same volume. Modular designs need space for the enclosure, the connector, maybe a little air gap for heat. So for a given size, you might get ten to fifteen percent less energy. For a phone or a pair of earbuds, that's a dealbreaker. But for larger devices like e-bikes or power tools, it's often a smart compromise. Luna: I've heard that modular batteries are easier to certify. Is that true? Lucas: It can be. When you use a standard cell that's already gone through transportation and safety testing, you're not starting from scratch. The UN 38.3 test for lithium-ion cells is brutal — vibration, thermal shock, altitude simulation. If you use a cell that's already passed, you still need to test your pack, but the cell-level risk is gone. That can shave months off your timeline and save you thousands in lab fees. Luna: But what about the actual user experience? Don't most people just want the thing to work, not to think about swapping batteries? Lucas: That's the thing. For some products, replaceability is a feature, not a bug. Think about a gardener using a cordless trimmer all day. With modular packs, they can carry two or three spares and never wait for a charge. That's a real selling point. But for a sleek consumer gadget, a visible seam or a removable door can feel cheap. So it's a design decision, not just an engineering one. Luna: Let's talk money. What's the cost difference for a startup making, say, an e-bike? Lucas: I've seen numbers where a custom integrated pack adds maybe thirty to forty percent to the bill of materials compared to a modular design using off-the-shelf cells. And that's before you factor in the tooling for a custom plastic shell. With modular, you can use a standard cell holder, a simple tray, and a connector that's cheap and widely available. Luna: So you're saying modular is cheaper upfront? That's the opposite of what I'd expect. Lucas: It's cheaper in the short term, yeah. But you also have to think about the total cost over the product's life. Let's say an e-bike battery fails after three years. With a custom pack, the manufacturer might have to replace the whole thing under warranty, and that could cost them three hundred dollars. With a modular design, a tech can swap out just the failing cells for maybe eighty dollars. That's a huge difference in warranty liability, and it's one reason some investors are starting to ask about repairability before they write a check. Luna: That's a great point. I've seen some funds that specifically look for products that can be repaired easily. They see it as a kind of insurance against returns. Lucas: Right. And there's also the regulatory angle. The EU's right-to-repair rules are pushing manufacturers to make batteries replaceable by the user or by independent shops. If you're launching in Europe, that's not optional anymore. Modular design makes compliance a lot easier. Luna: But what about the performance nerds? If I'm a power user, I want the longest range or the highest output. Doesn't integrated always win on paper? Lucas: Usually, yes, on energy density. But there are clever ways to mitigate that. For example, some startups use a modular pack that allows you to add more modules for extended range. So you might start with a single module that gives you twenty miles, then add a second module for forty. That's a flexibility integrated can't match. Luna: So it's not just about cost, it's about offering choices. Like a car with a bigger fuel tank option. Lucas: Exactly. And that can be a real differentiator in a crowded market. You can sell a base model and a long-range model without designing two different battery packs. Luna: But there must be some downsides beyond energy density. What about thermal management? Isn't it harder to keep a bunch of separate cells cool? Lucas: It can be, but it's manageable. In a modular pack, you have more opportunities for airflow between cells, and you can design the enclosure to act as a heat sink. The key is to avoid hot spots, which means you need good cell balancing. That's where the battery management system, or BMS, becomes critical. A good BMS will monitor each cell's temperature and voltage, and it can bleed charge from the hottest cell to keep them all in sync. Luna: And if the BMS fails? Is it easier to fix a modular pack? Lucas: Actually, yes. In a modular design, the BMS is often a separate board that you can replace without touching the cells. In an integrated pack, the BMS is usually buried under the cells, so you might have to replace the whole battery just to fix a tiny circuit. That's a classic example of why modular saves money down the road. Luna: So, for a startup that's just starting out, what's the smart move? Is modular always the way to go? Lucas: Not always. If you're building something tiny like a smartwatch or a wireless earbud, modular is a nonstarter. You need that custom shape to fit in a small form factor. But if you're building anything larger — a tool, a scooter, a robot, a medical device — modular is worth serious consideration, especially if you're on a tight budget and a tight timeline. Luna: And it's not just about the product itself. It's about the whole business model. You can sell replacement batteries as accessories, which is a nice revenue stream. Lucas: That's true. Some companies have built entire businesses on that. And with modular, you can also offer upgrades — say, a higher-capacity battery that fits the same slot. That keeps your product relevant longer, which is good for customer loyalty and the environment. Luna: I've also heard that modular batteries are easier to recycle at the end of life. Is that accurate? Lucas: Yeah, it's a big deal. When you have standardized cells, it's much easier to separate them for recycling. With a custom integrated pack, you have to break it apart to get the cells out, which is labor-intensive and sometimes hazardous. So modular design can actually reduce your environmental footprint and help you meet sustainability regulations. Luna: So it's not just a cost play, it's a green play too. That's interesting. Lucas: Right. And that's part of why we're seeing more investors and customers ask about repairability and recyclability. It's not just a nice to have anymore. Luna: Before we go further, I want to pause for a second. We've been talking about hardware design, and honestly, this kind of conversation is exactly why we do this show. And I know a lot of you listening are either building something or running a company. If these episodes help you make a better decision or avoid a costly mistake, that's the whole point. And we keep doing this because a small group of listeners supports us monthly through buy me a coffee dot com slash fexingo. It's not a big thing, but it covers the hosting, the editing, the research. So if you find value in what we do, that's one way to keep it going. Lucas: Yeah, honestly, it's what lets us stay ad-free and dig into the details. No pressure, but it makes a real difference. Luna: Alright, back to batteries. So, Lucas, you mentioned that modular can be a differentiator. Can you think of a real example where a startup won because of that? Lucas: There's a small robotics company I read about that was trying to get into the delivery robot space. They chose a modular battery system because they knew the robots would be out in the field all day and swapping a battery in thirty seconds was a huge advantage over waiting for a charge. They ended up beating out a competitor that had a custom integrated pack, not because their robot was faster, but because their uptime was so much higher. Luna: That's a great example. So it's not just about the battery itself, it's about the operational flexibility. Lucas: Exactly. And that's the kind of thinking that separates successful hardware startups from the ones that fail. It's not just about the spec sheet; it's about the whole product lifecycle. Luna: So if you're a founder listening, what's the one takeaway you'd want them to remember? Lucas: I'd say: don't default to a custom integrated battery just because it sounds more premium. Ask yourself how your product will be used, how it will be serviced, and what happens when the battery dies. Modular might be the smarter bet, even if it means giving up a little energy density. Luna: And it leaves the door open for future upgrades, which is always a nice problem to have. Lucas: Right. The battery is one of the few parts of a device that you know will degrade. Designing for that from day one is just good engineering.