Dual 18650 Battery Holders

I recently received another batch of holders for 18650 batteries, so I decided to put together a short review in case it comes in handy for someone.
I’ve reviewed similar holders several times before, so this one is more of an addendum to the previous reviews.


A little about the price. The listing shows a price of $0.63 each, but the seller has a slightly tricky policy: shipping to Ukraine costs $0.61, while shipping to Russia is free. However, the holder itself then costs $2.41, rather than $0.63 + $0.61 = $1.24.

The shipping cost depends on the quantity, but it doesn’t increase proportionally, so my order of 10 holders came to $7.88, or $0.79 each. At the end of the review, I’ll probably include a few links to alternative listings that might be useful.

Anyway, I ordered ten, waited a while, and picked up a bulky package at the post office. Inside was another package wrapped in soft white material for protection.


No complaints about the quantity; everything was as ordered.


Each one is packed in its own sealed bag with a QR code.


The holders are universal, meaning they support both parallel and series battery connections. Though it would be more accurate to say that the batteries are installed independently, and the markings inside simply indicate series or parallel connections.
The manufacturer is listed as Blossom, and I’ll come back to that toward the end of the review.


The contacts are steel and fairly stiff.


Most common 18650 cells fit without any problems, but I still recommend inserting the positive end first, followed by the negative end. That reduces the chance of scraping the insulation near the positive terminal. This has happened to me before because the holder contacts are so stiff. The result was spectacular in the literal sense: on a protected battery, it burned through the strip connecting the positive terminal to the protection board.


Speaking of protection, only unprotected batteries fit in these holders. What’s more, batteries with a button top won’t fit either—or, if they do, getting them back out will be quite a challenge.


Rather than beat around the bush, let’s move on to the tests. For this, I took the holder itself, one of the batteries, and a milliohm meter.
I measured the battery’s resistance, which came to 14.08 mΩ.


Then I installed the battery and took two measurements:
1. The total resistance between the bends in the holder’s spring contacts.
2. The total resistance between the solder terminals.


To make this easier to understand, I sketched a diagram showing that the total resistance between the solder terminals is more than twice the battery’s resistance.
But if you think that means everything is bad, here’s what I can say:
1. If you simply solder the holder to a circuit board, then yes, it’s bad, and I wouldn’t count on it handling high currents.
2. But if you solder near the bend in the spring contact, the resistance is actually quite low.
3. Compared with holders that use spring-shaped contacts, this one is excellent.


Just to double-check, I also measured the contact resistance without a battery, at two points:
1. Between the battery contact pad and the bend in the contact.
2. Between the battery contact pad and the solder terminal. As they say, the difference is clear.


So we can represent the situation schematically, and I’ll explain it here.
R1 and R2 are the resistance between the battery contact pad and the bend in the contact. I recommend soldering at this point when using the holder with high load currents.
For example, at a load current of 10 A, the voltage drop across each contact will be about 15 mV, which is quite low. But if you solder to the terminals intended for mounting the holder on a circuit board, the drop at the same current will be 85 mV (R1+R3 or R2+R4).
In the first case, at 10 A, each contact will dissipate 0.15 W and will stay almost cool.
In the second case, 0.85 × 10 = 0.85 W, which is much more and will cause increased heating.

Excessive heating gradually anneals the contact, reducing its springiness and degrading it until the holder—and possibly the battery as well—fails.

If you increase the load current to 20 A, the power dissipated by the contacts will quadruple, reaching 0.6 and 3.4 W.
The calculation is simple: multiply the resistance (0.0085 Ω) by the load current (20 A) to get the voltage drop (0.17 V). After that, we multiply the voltage drop (0.17 V) by the current (20 A) to get the power dissipated as heat (3.4 W).


Above, I suggested not using the contacts for soldering to the circuit board, but instead connecting at the bend in the spring contact, as shown in the second photo. Also, in some situations I had to use an alternative approach: I inserted a low-resistance tab between the contact and the battery. The increased clamping force also gave me better contact. I used this setup to test battery capacity under a high load current.


At the very beginning, I said that the holders were made by Blossom. Of course, there are no guarantees, but I had already reviewed other holders from this manufacturer, and they performed noticeably better than their more branded Keystone counterpart. See the full review.


Below are the test results at 10 A, measured between the battery and the holder contact at the bend. To put it in plain English, the Keystone holder measured almost 2.9 mΩ, while the Blossom measured 1.3 mΩ. The holders reviewed here were only slightly higher, at 1.5 mΩ.


And here's a photo comparing the holder under review with a couple of my test holders: the unbranded one is on the left, and the Blossom 3x18650 with test wires soldered on is on the right.


The Chinese sellers also offer similar holders with wires already soldered at the point of lowest contact resistance — link.


I don't recommend holders like these; the voltage drop across their contacts is very high.



Based on the test results, I can say that:
1. These holders are decent if you solder the wires close to the battery.
2. With the standard connection or when soldered to a circuit board, they shouldn't be loaded with high currents.
3. They hold the batteries very securely.
4. Long batteries, including protected ones, won't fit.

Would I recommend them? I think so, with the caveats mentioned above. At any rate, I use these holders often and am completely satisfied with them.

Now for the promised links.
1. A wide selection of holders from a trusted seller — link
2. Blossom holders in a different design, with better specs, in 1x and 2x versions — link.
3. Blossom holders in a different design, with better specs, in a 2x version — link
4. 4x18650 holders — link

That's all for now. I hope you found this review useful.