TPcell battery for a Milwaukee M12 tool

I got a new drill/driver at home—or, well, not exactly new, more like not very old. And it didn’t just show up on its own; I got it going myself. Anyway, I decided to buy an extra battery for it, and today I’ll tell you how that turned out.

A reminder: to keep up with new posts on the blog, I recommend following me on Instagram. I’ll post notifications about new articles there, and maybe write about something interesting too — link to the account

You can also subscribe to updates and new articles on the Telegram channel — https://t.me/KirichBlog


I ordered the battery from AliExpress, from the fairly well-known manufacturer TPcell. I’d already published reviews of their batteries, and I can say their quality is fine, so the question of where to buy one never really came up. On top of that, I had a coupon, so the battery cost me about $25.
By the way, the store still has a $1 coupon that works for this battery.

I could have bought a lower-capacity battery for a little less, or a two-pack, which would also have worked out cheaper. But I wasn’t interested in a lower capacity, and if I was going to buy one, I might as well get the bigger one. A pair would have been overkill.

It arrived quickly, though there was one odd detail: they sent something like a postcard by regular mail (I think it’s still lying around in a desk drawer), while the battery itself came by Meest Express. Strange, really—the Meest Express tracking works perfectly well, and the postcard actually arrived noticeably later than the battery.



It looks like a standard M12 tool battery.


The store page has an image listing the claimed protection features. To get ahead of myself, most of them aren’t actually there: inside the battery, there are just the cells and a temperature sensor. That’s it. And that’s normal—the original batteries are exactly the same.


But back to the battery.
It looks very neat and tidy, everything is straight, nothing sticks out, and there’s no unpleasant smell.
Below is a comparison with a standard (non-high-capacity) battery—in this case, an original one.

The battery is held in place by clips, and these are noticeably stiffer than on the original. It also takes a little more effort to remove than the original battery.


It came charged to about 50%, at least according to the drill/driver’s indicator.


Speaking of the drill/driver, a special thanks to the friend who helped me buy it. With the electronic loads I’m building at the moment, I do a lot of drilling and thread cutting. My small drill/driver died, and the big one is a bit cumbersome, so I decided to replace it.
I chose this particular model for a few reasons. Here’s why I didn’t get a brushless one:
1. It weighs almost the same.
2. Better, more consistent speed control at very low RPM.
3. A smooth clutch. Since I’m cutting threads, I don’t need POWER, and this clutch is genuinely great.
4. I specifically wanted one without hammer action. I have absolutely no use for it, and the mechanism is simpler and more reliable.
5. It’s quieter than a brushless model.

It cost me 2340 UAH plus about 250 for shipping. There were cheaper options, but they were either completely beat up or came with a lower-capacity battery.
From the photos, it looked like it had barely been used, so that’s why I bought this one.


By the way, the person who helped me buy it has his own channel, and he recently posted an unboxing video of a package that also contained my drill/driver. I’ve been using it for about a month now, so it’s looking a little more worn.


Chinese manufacturers never change their ways: to put the capacity in Wh on the label, they simply multiplied 12 by 6 and got 72 :)
Just in case, the correct calculation is (3.6 × 6) × 3 = 64.8 Wh.



The battery weighs almost 400 g. The original 2 Ah battery is noticeably lighter at 175 g, but its capacity is three times lower.


The initial voltage was 10.84 V, with almost no difference between the cells, although to be fair, I messed up the measurement of the first cell.
The thing is, I measured the first cell relative to the thermistor contact rather than the power contact, so the actual voltage is slightly higher (10 kΩ in series with the multimeter’s 10 MΩ input).
It’s convenient that the contacts for all the cells are brought out. I think it would be quite feasible to add a balancer to the charger. But as I mentioned, these batteries don’t have a protection board.


Naturally, I took it apart before testing because I wanted to see what cells were inside. The assembly is neat too, and there are cushioning pads.


At first, I thought the cell groups were connected 3+3—that is, three in series in the upper section and three in the base. But no, the wiring is clever: a pair of parallel cells at the top, a pair at the bottom, and one parallel group is split, with one cell at the top and one at the bottom.
Murata VTC6 cells, which in my opinion are more than adequate for a battery like this. I have no doubts about their authenticity so far.


Before testing, I fully charged the battery using its original charger, whose authenticity I have absolutely no doubts about. Charging took a little over an hour.


Next, I planned to improvise some contacts from pieces of nickel strip and start testing, but it wasn't that simple: the strip just wobbled around in the contacts.
I had to investigate, and it turned out that the contact assembly—or, more precisely, the contacts themselves—are made of thick metal but don't have very good spring properties. Just out of curiosity, I tried the original battery, and everything was fine there: the contacts clamp even strip about 0.2 mm thick securely. I also tried bending the contacts slightly with a screwdriver without taking the battery apart, and that was easy enough.
So, at this stage, it gets a fail.


The first discharge was done after charging with the original charger. For the subsequent tests, I charged it with a battery tester: charge termination voltage 12.6 V, charging current 3 A (the screenshot shows 3.05; that was accidental—owners of these testers will probably understand why), cutoff when the current dropped to 200 mA.


I discharged it in several modes: 0.2C twice, first after charging with the original charger and then after all the tests, charging it with the tester. I also discharged it at 0.5C, 1C, and 10 A. I wanted to try 2C, but the load can only handle 10 A. At least I ran the 10 A test twice; the first time I forgot to take a thermal image :)

So we get 6 Ah at the output, which tells us two things right away:
1. The cells are very likely genuine; I personally have no doubts.
2. The cells have the same capacity, otherwise I wouldn't have got 6 Ah.

The capacity in Wh is also fine—everything looks good, and it's even slightly above the calculated value.


The case temperature after discharging at 10 A was about 50 degrees. I didn't measure the cells themselves, but it's clear they were hotter, though I doubt by much.


After all the tests, I fully charged the battery with the original charger and measured its impedance.
1. The impedance of the parallel group is 6.5 mΩ, meaning 13 mΩ for a single cell. I checked my VTC6 reviews, where I measured 12.5 mΩ, which matches the cells installed here exactly. Yes, it should be 12.5/2 = 6.25, but this measurement was taken through the nickel strip.
2. The impedance of the split group is a little higher, around 8 mΩ.
3. Total impedance at the terminals is 28 mΩ.
4. The smaller battery's impedance is exactly twice as high.


Voltage after the tests. It looks like the third cell has drifted a little, but we need more data; perhaps I should run the battery through a few cycles with the original charger.


The original battery.
1. The contact marked T (the clone has no marking, by the way) is connected to a 10 kΩ thermistor, referenced to the power negative.
2–3. It seemed to me that the original battery has better balancing, but I only charged it with the original charger (I don't know whether it balances the cells), although the third cell here is also slightly higher in voltage.




Conclusions.
I really have just one complaint about this battery, and it concerns the power contacts that connect to the tool. Otherwise, in my opinion, it's excellent. Sure, you could complain that the latches are a bit stiff and so on, but to me that's minor stuff—they'll loosen up with use. The important thing is that it has decent, genuine cells. That said, this manufacturer usually uses either genuine cells or pretty good Chinese ones.


So, should you buy it or not? I don't know, but it works for me so far. As a spare, it's more than good enough, and it could even serve as the main battery, but the contacts need some attention.