Where This Guide Comes From
This guide is based on the build video Micah published on the EbikeSchool.com channel, which has more than 584,000 views. The premise is simple and a little surprising: you can assemble a 48V 20Ah battery for an e-bike or a small vehicle without ever touching a spot welder. The trick is that the cell modules arrive pre-welded, so the actual assembly is mechanical: match the modules, tin the connection gaps, solder the series links, wire the BMS and wrap the pack. We go through each step the way the video shows it, then add the practical notes from the discussion under the video — including the questions people kept asking about the welding and the BMS wiring.
What "Without a Spot Welder" Actually Means
The first question most viewers ask is whether the title is honest, and the creator answers it directly in the comments: the modules use Panasonic 18650B cells rated 3.4 Ah each, and thirteen modules wired in series give a 48V pack with 20.4 Ah of capacity. The cells are spot welded at the factory into ready-made groups, which is why you never need to weld anything yourself. What you do instead is connect the pre-welded modules together with solder and nickel strip, and that is where the real skill in this video lives.
That distinction matters if you are shopping for parts. A bare-cell build needs a spot welder, a fuse-wire setup or a lot of patience with a soldering iron and risks damaging cells with heat. A modular build like this trades those risks for a slightly higher part cost, because the manufacturer has already done the delicate welding. For a first battery, or for someone who builds packs occasionally, the pre-welded route is far more forgiving — which is probably why a six-minute build video picked up half a million views.
Start With Module Voltage Matching
Before anything is glued or soldered, Micah checks the voltage of every module and only proceeds when the readings line up. With a 3.7V nominal lithium cell, a freshly received module should sit in a narrow band around the same voltage; if one module reads noticeably lower than its neighbours, that is the one to flag before assembly, not after. Modules that arrive from the same production batch are usually close, but the check takes seconds and it is the cheapest insurance in the whole build.
This is the same discipline that applies to any multi-cell pack: cells in series share the same current, so a weak module drags the whole string down and makes the BMS work harder to balance. Matching voltage before assembly is not about being fussy, it is about not discovering an imbalance once the pack is wrapped, glued and installed in a bike. If you have a few spare modules, pick the ones that match most closely and set the odd one aside.
Arrange, Offset and Hot-Glue the Modules
The modules are laid out with alternating polarity — positive up on one, negative up on the next — so the series connections can run a short, clean path between neighbours. The modules are also offset slightly rather than aligned perfectly, which the video shows makes the interconnect area easier to reach and keeps the solder points away from each other. Before anything is soldered, the arrangement gets fixed in place with hot glue so nothing shifts while you work.
The hot glue serves two purposes. It holds the geometry so the nickel strips land where they should, and it adds mechanical strength to the finished pack — the glue line takes some of the vibration that a bare soldered joint would otherwise absorb. On an e-bike that lives on a frame, that matters more than it looks. Let the glue set fully before you start soldering, and keep a little glue at the edges of each module so the block behaves as one unit.
Tin Between the Cells, Never on Top
Here is the step that most home-builders get wrong the first time, and the video is explicit about it: you tin the gap between cells, not the top of the cells. A blob of solder sitting on a cell terminal is a weak, high-resistance joint and a heat hazard; a fillet of solder in the gap between two adjacent cells bridges the connection the way a weld bead would, with the heat carried by the nickel strip rather than dumped into the cell.
The technique in the video is to apply flux, feed solder into the small gap between the two cells and let it flow into a smooth bridge. It takes a moment of practice to get the amount right — too little solder and the joint is weak, too much and you risk a lump that interferes with the next cell. The creator's rhythm is short, controlled passes with the iron, letting each joint cool before moving on. If a joint looks dull or grainy, re-flow it before assembly continues.
Solder the Series Links the Low-Heat Way
The nickel strips that join each module into the series string are soldered with the same short-pass technique. The iron stays on each joint for only about two seconds at a time, and Micah uses a non-conductive tool — a chopstick works, and it appears in the video — to press the strip down while the solder flows, so the strip sits flat and the joint fuses into a single solder pool. The goal is a solid electrical connection without soaking heat into the cells behind it.
Two habits from the video are worth stealing. First, do the series runs in a consistent order — down one side, back up the other — so the strips cross the pack in a logical path and the solder joints are easy to inspect. Second, let the pack cool between sections; a hot pack makes solder flow poorly and stresses the cells. This is also where the offset layout pays off: because the joints are spaced out, you are never soldering two hot spots right next to each other.
BMS Wiring: 13 Groups, Two Thick Wires, One Thin Chain
The BMS in this build is mounted on the first cell group with double-sided tape, and the wiring follows a fixed pattern that is worth writing down because it trips people up. The thick red wire goes to the positive terminal of the 13th group, the thick black wire goes to the negative terminal of the 1st group — those are the pack's main power leads. The thin red balance wires then run in sequence from group 13 down to group 1, one per group, and the thin black wire completes the circuit at the negative side.
A commenter on the video asked why the BMS uses a separate balance wire per group instead of one jumper at the end of each module. The creator's explanation, and it is a good one: individual wires per group give the BMS a direct measurement path to every cell group, and they let each balance path carry more current than a single jumper chain would. It is the difference between a five-lane road and a one-lane road — the connection is electrically the same in principle, but the current capacity and the monitoring accuracy are not. Follow the exact order from the video and double-check each wire against its group before you wrap the pack, because a crossed balance wire is the classic silent killer of otherwise good packs.
Wrap, Shrink and Label: Two Layers at 90 Degrees
With the BMS wired, the pack gets wrapped in black foam first — a soft cushion that protects the cells and the balance wires from abrasion — and then finished with two layers of heat-shrink tubing applied at 90 degrees to each other. The cross-wise second layer is the part people skip, and it is the part that stops the shrink tube from splitting along its seam when the pack flexes inside a frame.
Shrink the first layer from one direction, let it cool, then slide the second tube over the pack perpendicular to the first and shrink that one too. A heat gun with a gentle motion beats a hairdryer for an even shrink, and you want the tube tight but not so hot that the foam underneath melts. Finish by labelling the pack — voltage, capacity and the date — because a bare black shrink-wrapped brick is impossible to identify later, especially if you build more than one.
When Does This Build Make Sense?
The modular route is not the cheapest way to a 48V battery, and it is not the lightest either — the pre-welded modules and the extra glue and foam add a little weight and cost over a bare-cell build. Where it wins is speed, safety and repeatability. For an e-bike conversion, a small scooter or a backup pack where the battery sits in a protected frame, a 20Ah 48V module build is a reliable weekend project with no welding learning curve and very little that can go wrong if you follow the wiring order.
If you are sizing a pack for a heavier vehicle or longer range, the same technique scales: more modules in parallel raise the capacity, and the 13-series architecture stays identical. That is the part that makes this build a good first battery — the skill transfers directly to larger packs, and once you understand series and parallel groups you can size a custom battery system to your actual load instead of buying off the shelf. For the sizing math and the charging setup, the guides on our insights page go through the numbers in more depth.
These are the most useful of the video's top comments, with thanks-only and argument threads left out on purpose. Micah from EbikeSchool.com replied to a couple of the threads, so those answers quote him directly; the rest are ours, written the way we would answer a customer on the shop floor.Source video: EbikeSchool.com — "DIY 48V 20Ah lithium battery without a spot welder using Maker Batteries" (youtube.com/watch?v=Xoc4LIy5SnI). Comment excerpts are quoted verbatim from the video's top comments; the original creator did not reply to these threads, so all answers are Dajiu Energy's own. Build figures are transcribed from the video's measurements.