Where This Repair Guide Comes From
Every step in this article comes from one source video — sixtyfiveford’s Revive DEAD Battery Packs - Rebuild Repair - Dewalt Milwaukee Makita Ryobi Bauer Ridgid 18v 20v 12v, which has been watched more than 1.4 million times. In the video the creator takes two dead packs — one that flashes and refuses to charge, one that charges but dies under load — and walks through diagnosing them, testing every cell with a multimeter, and doing quick repairs that go as far as replacing a single cell. The video makes the point up front: the same cells, the same construction and the same repair methods sit inside every brand, from a cheap Ryobi to a top-of-the-line Milwaukee. If you would rather watch the repair before reading the breakdown, the video is right here:
Two Ways a Pack Dies: Flash of Death vs Voltage Collapse
The video opens with two different failures, because they point to different causes. The first pack charges normally but only lasts 30–45 seconds on a tool before it shuts off — the voltage collapses under load. The second pack flashes its charger light and will never take a charge at all. Both are extremely common, and both are often repairable.
The collapse-under-load symptom almost always means one or more weak cells: the pack’s resting voltage looks fine, but a bad cell sags the whole string the instant current flows, and the tool’s low-voltage cutoff trips. The flash-of-death symptom usually means the pack’s voltage dropped too low for the charger to recognize it, or a single cell has died — the pack is trying to tell you it is out of balance or shorted. The diagnosis path for both is the same: test every cell individually.
Diagnosis Step One: The Jump-Start Method
When a charger flashes and refuses to charge, the quickest test is the jump-start method, which is all over YouTube and is shown clearly in the video. You take a known-good battery pack — size does not matter — and jumper it to the dead pack, positive to positive, negative to negative. Twenty to thirty seconds is plenty; you do not want to do it long. If the dead pack’s voltage was simply too low for the charger to recognize, the good pack pushes it back up into the charging window and the charger will then accept it.
The video calls this a band-aid, and that judgment matters: if the pack was just deeply discharged, it may come back fine, but if a cell is actually dead, the pack will fail again in the future. So the jump start is a diagnostic tool, not a fix — it tells you whether the BMS and charger are the problem or whether cells are. And the video is candid about the sketchy variants people use — paper clips and other improvised jumpers — while demonstrating the proper way with real jumper leads.
Diagnosis Step Two: Testing Every Cell With a Multimeter
The reliable diagnosis is to open the pack and test each cell individually. The video takes the dead packs apart and checks every cell’s voltage with a multimeter, looking for the outliers — the cell that reads far lower than its neighbors, or the group that sags under load. In the first pack the problem cell is found quickly; in the second, one cell has gone completely dead while its partners still hold voltage.
A simple voltage check on every cell finds most problems, because in a series string the cells should all sit within a few hundredths of a volt of each other. A cell that reads 0V, or 2V where the others read 4V, is the smoking gun. The video’s habit — mark the bad cells as you test them — is exactly right, because once the pack is reassembled you will not remember which one was which.
Replacing a Single Cell: The Cheap Repair
Once the dead cell is identified, the repair can be surprisingly cheap: the video’s example rebuild uses replacement cells bought for a couple of dollars each. The technique is to cut the old cell free from the nickel strip, fit the new cell, and re-weld or solder the tabs — ideally with a small spot welder rather than a soldering iron held on the cell for too long, since heat is what damages cells.
Two things decide whether a single-cell replacement is a good idea. First, internal resistance matters: the video’s commenters are unanimous that you must test the new cell’s internal resistance and pair it with cells of similar resistance, or you are setting the pack up for an early failure — tools draw serious watts, and a mismatched cell runs hot while the others coast. Second, cells in the original pack came from the same batch and have worn together; one or two replacements may work, but if the pack is old and cells are cheap, replacing all of them at once is the more reliable move.
Why the First Cell in the String Dies First
One commenter on the video makes an observation that matches what repair shops see: the failed cell is often the first one in the series. The explanation offered in the thread is overcharging — the cell nearest the charge terminal sees the highest voltage during charging, its chemistry overheats and degrades faster, and it becomes the pack’s weak link. The same failure pattern shows up in phones and every multi-cell product.
The practical lesson is that a balanced pack lives longer: if one cell drifts high, it bears more charging stress, degrades, and pulls the whole pack down with it. That is why the video’s simple fix — finding and replacing the outlier — buys real life back, and why keeping packs topped up and out of deep discharge is the cheapest maintenance there is.
Cell Choice: High-Drain Cells Only
When the video rebuilds a pack, the replacement cells have to be high-drain cells — the same class as the originals — and the video’s commenters underline why this matters. Laptop cells are the classic mistake: they carry high amp-hour ratings, so they look perfect on paper, but they can only handle a fraction of the instantaneous current that a power tool demands. Under heavy load a laptop cell sags, runs hot, and dies young.
The rule is to read the cell’s discharge rating, not its capacity: a power-tool pack needs cells rated for 15–30A continuous draw depending on the tool, and the pack should never be asked to exceed what the cells can supply together. This is the same thinking the video applies in the other direction — he points out that the same repair methods cover everything from 12V packs up to 20V, because inside, the brands all use the same 18650-style cells.
Harvesting and Repurposing Cells From Dead Packs
Not every dead pack needs a new cell. The video’s thread is full of people who harvest cells from packs whose BMS failed while the cells were still good — the circuit board dies, the cells hold charge, and the pack becomes a donor. Those cells get reused as replacements in other packs, or repurposed into flashlights, pumps, dog collars and whatever else runs on 18650s, as long as you pay attention to voltage.
The safety discipline for harvesting is the same as for building: test every cell’s voltage and internal resistance, reject anything damaged, and never mix cells with different characteristics in the same device. One commenter’s trick for stubborn cells — a dab of hot glue on the end of the cell, then a dent-puller tool to lift it out of a tight pack — is the kind of practical detail that makes repairs actually doable at home.
When to Fix vs When to Replace
The economics in the video are blunt and useful. Replacement cells cost a couple of dollars each, and the repair takes an hour or so — compared with $40–$60+ for a new pack from any brand. One commenter rebuilt two budget Makita packs that kept shorting under high-drain tools: the factory replacements kept failing, but a rebuild with decent cells outperformed anything the factory shipped. Another saved three solar lights from the dump by swapping their batteries for about $15 worth of cells, rather than spending $150 on replacements.
The honest caveats: manufacturers design packs so that the easy path is buying new, and a repair needs care, a spot welder (or solid soldering skills), and matched cells. If you are not confident soldering or welding near lithium cells, the safe move is to practice or buy new. But for anyone who can follow a multimeter and a welder, reviving a dead pack is one of the cheapest, most satisfying repairs in the workshop — and keeps perfectly good cells out of the landfill.
Safety Rules That Apply to Every Battery Repair
The video’s repair work touches live cells, and its thread repeats the rules that keep that safe: remove jewelry, keep a bucket of sand and a fire suppressant nearby, never puncture a cell, never short terminals, and test before you trust — voltage and internal resistance on every cell you keep. Soldering near a cell should be quick and low-heat, or replaced by spot welding entirely; a cell that is swollen, hot or leaking is not a project, it is disposal material, recycled properly.
If you would rather buy a fresh, professionally built pack than rebuild the old one, a replacement battery is exactly what we make. Dajiu Energy is a Chinese manufacturer building lithium batteries for power tools, e-bikes, RVs, homes, golf carts and portable applications since 2017. Our product range covers LiFePO4 drop-in replacement batteries, EV and golf cart batteries, wall-mounted home storage, portable power stations, commercial energy storage and battery swap cabinets — explore the full lineup in our product center, or browse more buying guides. If you do rebuild your own, we’d still suggest matching the video’s care — and if you’d rather not, tell us the tool brand, voltage and cell count and we’ll engineer the pack for you.
What Viewers Are Asking (Top Comments on the Video)
Where the creator replied, we quote his answer verbatim; where he didn’t, we give our own practical answer — the way we’d answer a customer on the shop floor. We kept only comments with real practical value and dropped the pure thank-you notes.
Source video: sixtyfiveford — “Revive DEAD Battery Packs - Rebuild Repair - Dewalt Milwaukee Makita Ryobi Bauer Ridgid 18v 20v 12v” (youtube.com/watch?v=cDcVMZax2KA). Comment excerpts are quoted verbatim from the video’s top comments; creator replies are quoted where they exist, and unanswered threads carry Dajiu Energy’s own answers. 1.4M+ views. sixtyfiveford diagnoses and rebuilds dead power tool battery packs across every major brand: jump-starting the charger flash, testing each cell, and replacing single cells to save the pack.