Enclosed 18650 battery holders with a switch, too :)

As promised, here's a review of the second part of the package with battery holders. This time I'll show you enclosed holders that might come in handy for various DIY projects.
This time, I'll not only take a look at them, but also do some measurements.

They cost $0.41 each, and shipping to my country was $1.37 for the first one, then about 50 cents for each additional one, so 10 came to $10.10 in total.
Shipping to Russia is cheaper for the first one, but each additional one costs a little more. Strange seller.

These holders were packed at least as securely as the previous 4x18650 ones, so the seller gets a small plus for that. I've received something similar before, but they were just rattling around in the box, and after a month in transit the cases were covered in scratches. I wouldn't say it was a serious problem, but it was unpleasant; they looked used.


They look very compact.


They're not much taller or wider than a pair of 18650 batteries, but they're noticeably longer. I've included the weight just in case someone plans to use one in a portable device where that matters.


There are finger grips on the cover, and the switch is on the opposite end.


The cover comes off very easily, which I consider a downside. The case is made of plastic, but it's not very rigid and flexes a little, though not as much as the Blossom holders I showed earlier.


The thing is, the cover has no grooves, so you only need to slide it a few millimeters to open it. That means it could open accidentally.


I've often criticized spring contacts (not to be confused with springy contacts), and today I can show you their resistance—the very thing I've been criticizing them for.


There's a marking inside the holder. Don't worry, your eyes aren't playing tricks on you—I fell for it myself while editing the photo :)
It looks like the marking was accidentally stamped twice, with a slight offset.


The switch is a standard, inexpensive one, covered by a small cap held in place by two pins that are slightly larger in diameter than the holes in the cap. You can also see the rather thin wires here.


A flat-top battery fits perfectly, while a button-top battery is much harder to insert. A protected battery probably won't fit at all. In terms of compatibility, springs are definitely better than springy contacts made from steel strip; here, the available space for a battery is limited by the physical dimensions of the case.


If you look closely, you can see how relaxed the spring is with the green flat-top battery and how compressed it is with the blue button-top one. The blue battery was quite difficult to remove, so I wouldn't take batteries like that out if I were you—or use flat-top batteries instead.


Now for the measurements.
1. Since the battery itself will add some parasitic resistance to the tests, let's measure it first. I got 13.6 mΩ.
2. Including the terminals, the resistance was 54.9 mΩ. The terminals account for 41.3 mΩ, most of which is in the spring.
3. A pair of batteries brings it up to 108.4 mΩ. Subtracting the battery resistance gives about 81 mΩ across all the contacts.
4. With the wires and switch included, the result is really bad, so it's best to replace them. The resistance is already high, and they make it another 1.5 times higher.

I wouldn't say it's all that bad: at a current of 1 A, about 0.08 V will drop across the terminals and springs. At 2 A, that becomes 0.16 V, or 0.32 W. Still, I wouldn't use holders like these at high currents.



Overall, these holders are about average quality. The wires should be replaced right away, but even with good wires, I'd recommend using them at currents up to 1–2 A. Above that, the voltage drop will become significant, and the springs may start to heat up noticeably.
All in all, they're fine for small DIY projects. For anything more serious, I'd look for something else.