Sanyo NCR20700B, interesting 20700-size batteries

Today I’m reviewing batteries that are, in essence, nothing particularly special: they can handle currents up to 15 A and have a capacity of around 4200 mAh. The only thing that sets them apart is their somewhat uncommon form factor, but as always, you’ll find out more in the review.


A few words about the price.
The title lists a price of €5.65, which is quite expensive, but the price drops noticeably when you order more
More than 10 pieces at €3.85 each
More than 25 pieces at €4.55 each

There are other options too, but the best deal is to buy 10 to 25 pieces at €3.85 each.

The first noticeable difference from the other batteries I’ve shown before is their bright red color.


The batteries have a typical capacity of 4250 mAh. Here’s a brief excerpt from the datasheet.


Yes, although these batteries use a standard form factor, it’s somewhat unusual: they’re just 2 mm larger in diameter and 5 mm longer than the familiar 18650s. They may well fit in place of 18650s in some devices, especially those designed for protected 18650s (which are longer).
Batteries of this size are made alongside the 21700 format, but they’re less common. Perhaps 21700s are simply being promoted more aggressively.

Below, I’ve taken a photo comparing the sizes: 26650, 21700, 20700, and 18650.


According to the 7Z17 marking, the battery was manufactured on December 17, 2017. There’s a laser engraving on the negative terminal.
These batteries also have a matrix code to protect against counterfeits; the code is unique to each individual cell. The positive terminal protrudes noticeably beyond the front of the casing.


According to the description, the battery should weigh no more than 63 grams, so this one is fine.


"Training" run showed a capacity of around 4400 mAh at a discharge current of 500 mA, which is perfectly normal considering that this charger reads high

Based on their specs, these batteries are more in the "medium-current" class, alongside better-known models like the Samsung 30Q, LG HG2, and Murata VTC6, so I used an EBC-A20 load for the test.


The charging mode for these batteries is CCCV, with a charge current of 2 A (0.5C). Charging ends when the voltage reaches 4.2 V and the charge current drops to 80 mA. In my case, the lowest cutoff current I can set is 100 mA, but my previous tests have shown that the difference in the results is very small.


A full charge takes more than two and a half hours. Since the actual charge current is below 0.5C—the battery capacity is over 4 Ah—that’s about right.


Above, I included the discharge graph from the datasheet, which shows tests at 1C, 8 A, 12 A, and 15 A. I ran more tests: 0.2C (0.8 A), 0.5C (2 A), 1C (4 A), 2C (8 A), 3C (12 A), and 15 A. The description also included a graph for 20 A, so I tested that too.


At 0.2C, the capacity came to exactly 4200 mAh, or 15.22 Wh. At the maximum current of 20 A, the result was naturally worse: 3943 mAh (12.59 Wh). But at 15 A, the battery delivered the 4000 mAh specified in the datasheet.


The battery gets quite hot. The thermal image below shows a temperature of 67 degrees at 12 A, close to 82 at 15 A, and just over 100 at 20 A. So its actual continuous current is 15 A, which is also what the manufacturer’s main graph specifies.


The second battery performed slightly better, but I was more surprised by the "hump" at the start of the discharge at 20 A. No, this is normal in itself: first the voltage drops, then self-heating begins, causing the voltage to rise, followed by the more familiar drop as the battery discharges. But the first battery didn’t do this, and I have no idea why.


The temperature was only slightly higher at 12 A; at 15 A and 20 A, it was the same as with the first cell.


The specs and test results all look great: current up to 15 A, capacity of 4200 mAh, and a size only slightly larger than an 18650. But when I got to the graph showing cycle life versus discharge current, I was a little disappointed.
With repeated cycling—that is, charging and then fully discharging at 12 A—the battery loses two-thirds of its capacity after 500 cycles. At 8 A, its lifespan is noticeably better.
But keep in mind that these figures are for continuous charge-discharge-charge-discharge cycling, not charge-discharge-pause-discharge, and so on. In real-world use, the results will be better. This is because during cycling, the temperature will be noticeably higher, and temperature is the main enemy of long service life.


The usual internal resistance measurement: as received, after “conditioning” and a full charge, and after all the tests. You can see that after 8 full cycles, one of which ended at 100 degrees, the resistance had increased slightly.


I spent a long time thinking about which batteries would make the fairest comparison for this one, and concluded that it should probably be the Samsung 30Q, as a “peer” of the battery under review, though it has lower capacity because of its smaller case, and the recently introduced high-current 21700 Molicel P42A.
It turned out that at load currents up to 20 A, the Sanyo matches the high-current P42A in capacity in mAh, but falls slightly behind in Wh—which is understandable, since they belong to different classes. The Samsung, meanwhile, lags noticeably behind on both counts, with the difference reaching almost 1.5 times at a current of 0.2C.


To sum up everything above:
Overall, these are decent batteries, with a good balance of capacity, size, and price. Nkon also offers quantity discounts. However, their somewhat unusual size may be a drawback. If you can fit a 21700, that would be the better choice.
You may be wondering where you could use them. I can think of three applications:
1. Electric vehicles
2. Power tools, especially when 18650 cells leave a lot of unused space in a rebuilt battery pack, but 21700 cells won't fit.
3. Vaping, though of course your box mod needs to support this size.

If you need “more current,” there's the NCR2070C model, with a capacity of 3500 mAh and a current rating of up to 30 A.

Personally, I see these as an option for rebuilding batteries for cordless drills and other tools. Often, 18650 cells leave a lot of free space in the battery case, so this lets you get more capacity. For example, 2×20700 cells give you 8.4 Ah, while 3×18650 cells give you only a little more—9 Ah.

That's all for now. Next, I plan to put together a roundup of all the batteries I've tested this year, and then I'll probably leave this type of energy storage alone for a while :)