Molicel INR21700-P45B 4500mAh batteries - 45A

By a twist of fate, I got my hands on one of the new batteries from Molicel. It’s a very interesting cell, mainly because it combines relatively high capacity with a high rated discharge current. Inspection, tests, comparisons, conclusions—as usual.

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I’ll explain at the end how this battery came into my possession. For now, let’s get to the subject of the review.

I’ve already reviewed batteries from this manufacturer. I’d put them a little above average—not Samsung or Murata, but still very good.
Molicel INR18650-P28A
Molicel INR21700-P42A

The new model looks just like the INR21700-P42A


I found the datasheet on the manufacturer’s website without any trouble. The page for this model asks you to register and request it, but Google also turned up a direct link to the file itself.



The heat-shrink sleeve has the model marking, presumably a production date code, and a matrix code, so it’s easy to spot a counterfeit.


The dimensions match the datasheet, but the cell weighs a little less than specified, which is a plus for its intended use.


The battery arrived almost fully charged, but I still ran a “normalization” cycle, which yielded slightly more than the rated 4500 mAh.


Two main charging modes are specified: normal charging at 4.5 A (1C) and fast charging at 13.5 A (3C). The datasheet also includes a graph for 2C charging.
Charging terminates when the current drops to 0.05 A.


In normal mode, charging took 1 hour and 15 minutes—a fairly average result. I expected the CV phase to be shorter.


With fast charging, the battery reached a full charge in half an hour, which is about what I expected.
The datasheet says to stop charging when the temperature reaches 70 degrees. In practice, the temperature at the CC/CV transition didn’t even reach 50, which is excellent: that leaves 20 degrees of headroom for a higher ambient temperature.


But the battery’s key feature is its rated continuous discharge current of 45 A, which is a lot. The datasheet does caution that discharge should stop at 80 degrees, although its own graph shows results for what appears to be a full discharge cycle.


I tested it at almost the same rates, but added a 0.5C test and measured at 0.2C (9 A) instead of 10 A, where C = 4.5 A. Unfortunately, my load can handle a maximum of 40 A, so I couldn’t test at 45 A, but I doubt the difference between 9C and 10C is that significant. All tests were run at an ambient temperature of 23 degrees, exactly as specified in the datasheet.

The discharge results look pretty good to me. The energy delivered in Wh does drop off a little, but that’s normal.


The temperature results are a little more complicated.
I measured the temperature at the very end of discharge at 20, 30, and 40 A. As mentioned, the manufacturer says to stop discharging at 80 degrees. I didn’t stop the test; I simply noted how long it took for the temperature to reach that value. At 30 A, the battery was at 80 degrees by the end of discharge. At 40 A, it reached that temperature 4 minutes and 30 seconds after the test began, or about three-quarters of the way through.
I’d originally hoped the temperature would stay below 80 degrees at 40 A, but at that current the battery heated up to almost 100 degrees.


As always, I tested the remaining capacity after discharging at the maximum current and got another 90 mAh. Neither a good nor a bad result—somewhere in the middle. For example, the high-current Vapcell T39 21700 3900mAh delivered 65–75 mAh.


As an extra, I decided to run three more tests, this time discharging at a fixed power of 25, 50, and 100 W. This is a little easier on the battery, since the current only reaches its maximum toward the end of discharge. In general, this discharge mode is closer to the typical operating conditions of electronic devices, but specifications are usually given for constant-current discharge.



Temperature at the end of discharge at 50 and 100 W. Note that at a 100 W load, it stayed below 80 degrees, which is good.


I found information in the datasheet about operation at various temperatures down to -60 degrees, as well as the relationship between cycle life and load power. Interestingly, the manufacturer specifies performance here for discharge down to 2.65 V, not 2.5 V, and cutoff at 83 degrees, not 80.


Impedance after the “conditioning” cycle and after all the tests—no questions there, everything matches the datasheet.


Of course, I wanted to compare it with other batteries. There were plenty of candidates, but I decided to pick two: the previous model, the 42A, and the Vapcell T50, which is based on Samsung’s flagship 50S cell.
Comparison at 0.2C, 10 A (9 A), and 20 A. Unfortunately, I didn’t have an EBC-A40L load at the time, so the limit was just 20 A.
1. Molicel INR21700-P45B - blue
2. Molicel INR21700-P42A - red
3. Vapcell T50 - green

At the specified operating points, the batteries under review predictably landed in the middle. The 42A fell behind because it has lower capacity to begin with, while the T50 pulled ahead, as it is rated at 5000 mAh. However, its maximum continuous current is specified as 35 A, so it would have a harder time at higher currents.


And now for some background.
Someone contacted me asking me to test these cells. They make batteries for drones used by our military. The problem is that the operating conditions are very demanding and, as I was told, current draw during sharp maneuvers can reach 100 A per battery, or 50 A per cell, with total power consumption jumping to around 2 kW.

As always, the challenge is finding a battery with the best balance of performance and price. You could use pouch cells, but they cost more. These cells, on the other hand, offer very good current delivery at a lower price.
And speaking of current delivery: yes, the battery can handle 50 A, I think without any problems. But I’m personally concerned about the temperature, since it will of course be higher in a pack than for a single cell sitting on a bench. It all depends on the average discharge rate, though, not the peak loads.


And here’s the platform for the “birds” that these batteries go into.


And this is something I write about often: the discharge curve for each battery model is usually unique. Here, for example, are the curves for the batteries from this review—the manufacturer’s and mine—with the characteristic bends visible in both cases.


Conclusions.
Compared with the previous model, the new one is clearly better—not only in the capacity it delivers, but also in how its voltage holds up under load. For example, halfway through a 20 A discharge, the 42A cells were at about 3.422 V, while the 45B cells were at 3.486 V. In a 6S battery, that gives you an extra 0.4 V, or about 8 W of power.
Looking at these cells on their own, I was a little disappointed. They’re rated for a continuous current of up to 45 A, but in reality they can deliver up to 30 A continuously without overheating—and that’s not even in a tightly packed battery.

That’s about it from me. I hope you found this useful, and as usual, I look forward to your questions and comments.