Anyone who has ever tried to solder a wire or metal strip to a battery will know that this is near to impossible. What you really need for such a repair job is a spot welding tool. This is where the Fnirsi SWM-10 comes in.

Battery packs have invaded our world with the rise of cordless electric garden tools, electric bicycles, scooters, cars and what not. Cells in battery packs are spot welded together with strips of thin metal. When done properly, this creates good, strong joints without damaging the battery. The inconvenience is, however, that it is difficult to replace a dead cell without the right tools.

Don't Solder, Weld!

Anyone who has ever tried to solder a wire or metal strip to a battery will know that this is near to impossible. At best, you obtain a fragile joint that falls off as soon as you pull on it, but it is more probable that the battery explodes in your face while you overheat it. Adhesive tape or chewing gum usually gives better results.

What you really need for such a repair job is a spot welding tool. This is where the Fnirsi SWM-10 comes in. The Fnirsi SWM-10 is a portable spot welding ‘machine’ the size of a small multimeter. It is intended for building and repairing battery packs, but as you may not do that every day, it doubles as a 5000 mAh USB power bank.

welded 4 layers
The Fnirsi SWM-10 is specified for welding nickel, iron and stainless-steel sheet with a thickness of up to 0.25 mm. I tried, and it works.

Unpacking the Fnirsi SWM-10

In the box you find, besides the device itself, two thick cables (8 AWG, approx. 30 cm long), two spare welding tips, a USB-A-to-C cable, a roll of sheet metal strip (10 mm wide, 0.1 mm thick, nickel?), and a multilingual manual. I didn’t unroll the metal strip, but from measuring its circumference and estimating the number of windings, it appears to be some 5 m long.
fnirsi swm-10 box contents
This is what is included in the box.

The SWM-10 looks rather sober, all black, with a black window and three pushbuttons. The two sockets for the welding cables are in the left upper corner. On the rear is a foldable stand. The power button is on the top side of the SWM-10, next to the USB connectors and a reset pinhole.

Intuitive Display

After switching the device on you discover a 1.8” color display showing several values. These are actually easy to understand as they consist of four user-adjustable parameters (preheat time, pulse length, pulse interval, and dots) and status information (battery voltage, temperature, sound on or off, current and a spot-weld counter). With the left/right button you move the cursor up and down (really), while the up & down buttons let you adjust the selected value (shown in yellow). A long press on the left/right button opens (and closes) the settings menu.
fnirsi swm-10 color display
Colorful display.

A short press on the power button brings up (and closes) the charge/discharge screen. Here you can see how much energy is left in the battery and if and how the charging is progressing.

The manual is brief and only explains what the values and parameters mean and what the buttons and LEDs are for. There are no instructions on how to use the device for welding, so I had to find that out myself. The only instructions I found were that you should charge the battery before welding and that for best results you should not press too hard on the nickel strip when welding.

How Easy Can the Fnirsi SWM-10 Be?

As it turns out, it is extremely simple to use the Fnirsi SWM-10, and this is probably why they claim it to be intelligent. All you have to do is place the two tips one after the other on the workpiece (do not press too hard) and wait two seconds. Then you will hear a soft kind of click sound and that’s it. The number of clicks you hear is determined by the value of Dots (1 to 5).
this is how you do it
This is how you weld. Press lightly and wait a few seconds.

The default values worked fine for me when welding a piece of nickel strip to a button cell. Pulling the strip off again required force. For stronger joints you can make the pulses longer and increase the number of dots. Be careful, though, with high values, sparks and smoke begin to appear and the underlying surface may be burned or damaged otherwise. I’d suggest wearing goggles to protect your eyes. Also be careful when working with sheet metal this thin, as it is very easy to cut yourself with it.


The Fnirsi SWM-10 is an excellent tool for anyone who has been confronted with a battery pack with a dead cell in it and didn’t know how to fix it. Battery packs tend to be costly. Even repairing only one is probably enough to justify buying this inexpensive tool. Of course, once you have one, you can also assemble your own battery packs or use spot welding for other projects. And don’t forget that it is also a 5000-mAh power bank.

Tag alert: Subscribe to the tag Review and you will receive an e-mail as soon as a new item about it is published on our website!