A Pair of Cordless Screwdrivers

It’s no secret that a cordless screwdriver is a useful tool around the house, so I decided to test—and, more interestingly, compare—these two tools from a Chinese brand with the rather odd name LOM YUM.
This review covers everything: an inspection, teardown, tests, a comparison, and a small bonus.

When choosing a tool to review, one of my key requirements was that it come with two batteries. In my opinion, using a cordless screwdriver (or any cordless tool, for that matter) with only one battery often turns into a real ordeal.

As I mentioned, there are two screwdrivers in this review. They differ in many ways: battery voltage, number of speeds, design, and how the charger connects. Their only common feature is what they’re designed to do.

They arrived together in one box, and I was a little surprised by its size. The “Small Packet” label was especially amusing :)))


I’ll start with the larger model.
The screwdriver comes in a plastic case.


Everything inside is laid out fairly neatly, with dedicated spaces for the screwdriver itself and the spare battery. The charger doesn’t have its own compartment, so it can rattle around in the case. Another downside is that the molded hinge connecting the two halves is quite stiff, and the case tends to close by itself unless you force it open all the way.


The package includes:
1. The screwdriver with a battery installed
2. A spare battery, identical to the one installed.
3. A charger
4. Instructions
5. Two double-ended bits
6. A case to store all this stuff.


The instructions are entirely in Chinese, so the pictures are about the only useful part. Still, I don’t think it’s hard to figure out how to use a screwdriver.


The charger has a flat-pin plug and connects to the battery via a barrel connector. There are no labels or markings on it; it just says 18 V, and that’s it.
There’s an indicator on the opposite side.


To assess the build quality, I took the charger apart and inspected it. I’ve tucked the whole process under a spoiler.

The battery is rated at 21 V. In reality, the manufacturer is being a little misleading here by quoting the voltage at the end of charging. Incidentally, the charger stops charging at 20.8–20.9 V.


I wasn’t keen on the charger connecting via a basic plug, though. I prefer chargers that the battery slides into. Another option is a charger that doesn’t get in the way while you’re using the tool—that is, one that connects underneath or on the side.


We’ll take the battery apart too, of course.

The kit also included two bits: one universal bit for both flathead and Phillips screws, and another with a symmetrical Phillips design.
The finish is so-so, but in practice they turned out to be pretty good bits. At least they fit the screw heads properly.


And now I’ve finally got to the drill itself. The first thing to say is that the color really stands out, so it’ll be hard to lose :)


The battery detaches, as was clear from the start. For the first 20 or so times, it was quite stiff. I’m more used to batteries that click into place easily, in one motion, but after a while everything settled in—the battery packs wore in against the drill, or maybe the other way around.


The drill has only one speed, with a range of 0–650 rpm. In my opinion, this is a pretty convenient range. It covers most needs without having to switch speeds. I might have preferred a maximum speed of 900–1000 rpm, but that would have noticeably reduced the torque.
The manufacturer has tried to «kill two birds with one stone», but we’ll put that to the test.


The handle is rubberized, and there are plenty of rubber inserts, so when you set the drill down on a table, it rests on those inserts rather than on the plastic. Though personally, I don’t think they add much.


There’s an LED work light above the trigger. It’s fairly bright and reasonably well focused, but unfortunately it goes out as soon as you release the trigger :(
There’s also a rubber insert at the back that covers the entire rear section, although the build quality leaves something to be desired—the fit isn’t particularly precise.


The torque clutch has 21 settings plus a drilling mode, although I never use that mode when drilling.
I couldn’t find any information on the torque value, and the store page says “The 21N.M torque setting,” which seems more likely to mean that the drill has 21 clutch settings.


The chuck is of average quality; I didn’t notice any runout. Its maximum capacity is 10 mm. 13 mm would of course be better, but that’s much less common.
You need both hands to tighten the chuck, which is a problem with almost all inexpensive drills. That’s because they don’t have a spindle lock, so the spindle turns when you rotate the chuck.
This drawback is common to all drills with a two-piece chuck.


That wraps up the external inspection of the first test subject. On to the second.
This «fellow» also comes in its own plastic case, though it’s a little smaller.

The store listing is called LOM YUM Electric Drill, and the price is $48.80, but with the gbblom coupon you can get it for $33.39.


Unlike the first case, the molded joint between the two halves here is much more flexible. I haven’t tested it in low temperatures, but I don’t think it would hold up well; in warm weather, though, it should be fine.


There are separate compartments for the drill and battery here too, and the manufacturer hasn’t forgotten the charger, which has its own slot. That’s a plus.


The package is exactly the same as the first one:
1. Drill with battery installed
2. Spare battery, identical to the one installed.
3. Charger
4. Manual
5. Two double-ended bits
6. Case for storing all this stuff.


Unfortunately, the manual is still in Chinese, so it’s just as useless as the last one.


This one has a more familiar-style charger: the battery goes into the charger, rather than the charger going into the battery, as with the previous drill.
Charging time is about the same as for the previous one, around 1 hour 20 minutes.


This charger didn't escape disassembly either; the results are hidden under the corresponding spoiler.

This battery has four cells, rather than five like the previous screwdriver, which explains the stated voltage of 16.8 V.
I honestly tried to open it, but unfortunately, I didn't succeed.
The case consists of two “cups,” with one fitting inside the other.
There are four tight clips along the sides of the “cups.” I managed to “disarm” two of them by inserting pieces of some discount card, but I couldn't release the other two, which have to be pressed at the same time. I couldn't even get one of them to disengage.
But I did manage to find out a few things. The cells look exactly like the ones in the previous battery. Also, knowing the cells' length and seeing their ends, I can assume there's a protection board near the contacts. The fact that a temperature sensor is just visible inside (there is one in the previous battery) also suggests there's a board.
Neither screwdriver has cell balancing; the controller only monitors the individual cells.


This screwdriver came with exactly the same bits as the larger one; they're at the top of the photo.


This screwdriver is a little smaller than the previous one, but for the most part, the main difference is the battery design.
Personally, I prefer screwdrivers that can stand upright, like the previous one, but it's a matter of habit. I know some tradespeople always try to lay their screwdriver flat for safety. This one is better suited to that.


Although this tool is smaller, it already has a two-speed gearbox, so there are two speed ranges: 0-350 and 0-1350.
The first is better suited to driving screws and drilling with large-diameter bits; the second is for everything else.


As I mentioned above, this drill has two speeds, so it has the corresponding switch on top.
There is also a battery charge indicator on the side. It lights up when you press the trigger, but its readings are very rough, so I wouldn't rely on it too much, even though it's handy to have.


As with the previous model, there are plenty of rubberized areas on the housing, but here the coating has a fine mesh texture for better grip. We'll see how long it lasts :)

The store page has a nice picture showing this drill being submerged in water. That's complete nonsense—how can you use a tool underwater when it has open ventilation slots?
And the line “IPX7 waterproof, can use it on a rainy day” made me laugh. To translate it roughly: our tool has an IPX7 protection rating (brief immersion to a depth of up to 1 m), so you can use it on a rainy day :)


Like its “big” sibling, this one has an LED to illuminate the work area, but in practice it makes little difference whether it's there or not. It's much less effective than the one on the previous model, and it also goes out as soon as you release the trigger.
The torque adjustment has 18 settings plus a drilling mode.


The chuck is generally comparable in quality to the one on the previous model, but its plastic part is slightly out of balance, although the chuck itself has almost no runout.
The maximum clamping diameter is 10 mm.


Before moving on to a more “in-depth” description, here's a comparison photo of both test subjects.


A little about ergonomics.
First, the weight.
The larger drill weighs a little over a kilogram—about 1150 g with the battery, which itself weighs around 330 g. I'd put it in the mid-range class: on “heavy-duty” models, the battery alone can weigh 700-800 g, and the drill itself weighs over 2 kg.


The second one is a little smaller. With the battery installed, it weighs just under a kilogram, while the battery weighs a little over 200 g. This partly suggests that the first drill's battery is a bit better protected; here, the tool's handle itself provides some of that protection.


Ergonomics, though, aren't as straightforward as they might seem.
For example, I much prefer the larger one. Or rather, it's not that I like it more; it simply sits much more comfortably in my hand, mainly because of its thinner handle. Also, in reverse, the switch presses against my knuckle, which isn't very comfortable. The only consolation is that the tool is used in reverse much less often.
In my opinion, the tool should sit in your hand as shown in the top photo. It's noticeably easier to hold (and keep hold of) that way, and your hand gets less tired despite the extra weight. So the smaller one is better for short jobs, while the larger one is better for bigger tasks.


And now we've finally reached the teardown of our “patients.”
A tool like a cordless drill/driver is pretty simple inside, so this won't take long.

First up was the big one


The rest of the teardown is hidden under the spoiler.

The second one on the operating table.


The rest of the teardown is under the spoiler.

A side-by-side photo with both tools disassembled. As you can see, they’re identical in terms of power; the only key difference is that the smaller one has a two-speed gearbox.


Checking the battery capacity.
For this test, I used the battery tester from this review. It wasn’t very convenient to connect, but that’s how it goes.
During testing, I noticed that each battery has an automatic low-voltage cutoff, but after 5–10 seconds the circuitry applied voltage to the terminals again.
The smaller battery charges through one set of terminals and discharges through another. The larger one is the same, although it has a clearly visible separate socket.


The larger battery delivered 1265 mAh. But then I tried discharging it a few more times (the screwdriver still worked quite well after the protection kicked in and was reset) and got another 60–80 mAh out of it, which suggests the battery capacity is over 1300 mAh.
The product page also listed the capacity as 1300 mAh, so I don’t understand why they put 2 Ah on the battery pack.
The protection circuit cuts off the battery at around 14.7 V, or about 2.95 V per cell.


The smaller screwdriver’s battery delivered more capacity: around 1330 mAh before the protection first kicked in. If you try discharging it a few more times, you can squeeze out 1380–1400 mAh.
The protection circuit cut off the battery at around 12.3 V (as shown on the graph), or about 3 V per cell.


Now that the experiments are done, I’ll move on to some “field” testing. In my opinion, that’s the best way to assess the tools’ capabilities, battery capacity, and ergonomics.
For the test, I bought 300 4×50 screws with coarse threads for wood. Since I wasn’t sure that would be enough, I also dug out a packet of about 100 4×51 self-tapping screws from the cupboard. They have a thicker shank than the screws I’m using, so they’ll put the tools under more load. I also bought a 2000×150×50 pine board, which turned out to be 145×45 rather than 150×50. Sorry, the board isn’t in this photo :)


Other test participants:
1. A 16 mm spade bit.
2. A 35 mm Forstner bit
3. A 6×70 screw
4. An 8×70 screw
5. A 5×120 screw


Before the “field” battery-capacity test, here’s a short video showing how the screwdriver performs in different modes.
In the video, I tried to show drilling with a spade bit and a Forstner bit, as well as driving screws of different diameters. I pre-drilled shallow 4 mm holes for the 6×70, 8×70, and 5×120 screws; otherwise, driving fasteners like these into a piece of wood is very difficult.


The screwdriver drove all the fasteners flush without much trouble, although the clutch was set almost to maximum.
The Forstner bit was the only thing it struggled with. To be fair, I hadn’t tried drilling wood with one before—usually I use it on chipboard or MDF.


For the next test, I first marked out the board to make it easier to drive the screws. I left plenty of room, since I had to test two screwdrivers.


A single battery was enough for 390 screws: 298 wood screws and 92 self-tapping screws. The self-tapping screws were about one and a half times harder to drive, and the difference was quite noticeable.


As I mentioned above, the drills have motors in the same class, so their power should be roughly the same. But the test revealed some noticeable differences.
Given that the smaller drill has a lower speed (in first gear) despite having a comparable motor, it should have more torque. But in practice, things turned out a little differently.
It performed noticeably better when drilling, thanks to its higher speed, but it struggled more with the Forstner bit, and the clutch kept trying to engage.
The results with the large screws were also mixed. Even with the torque limit set to maximum, the clutch still kept engaging. This is clearly visible in the video, so I eventually switched to drill mode, which disables the clutch. It was tough, but it worked.
Surprisingly, the 120 mm screw went in without any trouble.


The result.


But this drill really surprised me in the battery capacity test, to say the least.
Knowing roughly what this tool could do, and comparing the previous drill's result with its battery capacity, I marked out 300 spots on a board and started driving screws in one after another.
I was already a little tired (390 screws driven in and 389 backed out), so I was hoping to finish quickly and go have dinner—it was evening, after all.
But that wasn't to be. First, I ran out of wood screws, which was predictable. Then I ran out of marked spots and started driving screws in, spacing them roughly the same distance apart.
After the fourth hundred, it was starting to get on my nerves, but I kept going. Then I ran out of the screws I'd prepared.
My first thought was that the battery controller had failed and the automatic shutoff wouldn't kick in.


But it turned out to be simpler: I took the battery and went to discharge it using a battery tester. After discharging 13 mAh, the battery protection cut off the discharge.
But since the protection reconnects the battery afterward, I went back and drove in four more self-tapping screws. That was it—the battery gave up. So the total was:
I drove in 417 screws and self-tapping screws, then discharged 13 mAh, which is 1% of the capacity (equivalent to 4 screws), and after that drove in four more. That makes 417+4+4=425 screws in total.
I don't know how that happened. Based on the previous review, the drill should have given up another hundred screws ago, but it just kept going. Maybe the board was well dried, maybe the screws were different, but the result speaks for itself: the larger drill drove in 390 screws, the smaller one 425, into the same board. And in the second test, I ran into resinous knots more often.


At the end of the tests, I measured the tool's temperature. I drove screws continuously, but the temperature remained perfectly normal.


What can I say in conclusion.
During the main part of the test (driving a lot of screws), I drove in 815 screws and removed 813 (two are still stuck forever in resinous knots), so I can now confidently draw some conclusions about ergonomics.
The orange drill driver did pretty well in terms of comfort. Its better weight distribution when held vertically made a difference: the center of gravity is right over your hand. The thinner handle also made it more comfortable to grip. Screws went in faster thanks to the higher RPM. As you can see in the video, it handled all the jobs I put it through without any problems. The only downside was that the battery ran out a little sooner than I expected.

The blue drill driver had noticeably better battery life, which I really didn't expect. But it was less comfortable to use, though that was clear from the start. Its weight distribution is worse, and you can feel it a little when holding it vertically. In the horizontal position, there's no difference compared with the orange one. My hand also got more tired because the grip is less comfortable, so it may not be ideal for extended work. But the biggest nuisance was the direction switch. I used the same drill driver to remove the screws as I had used to drive them in, so I could judge how comfortable it was to use. When backing screws out, I kept accidentally switching it into neutral with my hand, which was a bit annoying. On the plus side, removing screws was faster because I switched it to second gear for that.
With the same motors and a higher reduction ratio, it has less torque than the orange one, which is very strange.

Things both drill drivers have in common.
The chucks on both drill drivers can loosen when reversing and when the clutch ratchet engages, though this happens less with the orange one. Tightening the chucks is awkward on both, but that's partly because I'm used to working with a drill driver that has a spindle lock. It's very hard to get used to doing things differently.
Over time, the battery packs on both drill drivers started latching and unlatching properly. At first, you had to apply noticeable force, but that's normal.
The work light is quite handy, but the blue one is noticeably dimmer. On both drill drivers, the light turns off as soon as you release the trigger.

That's almost everything. As always, I'll be waiting for your questions in the comments.
By the way, if you use the BTS10OFF coupon on the first drill driver, it'll cost 10% less.

As a little extra, here's a very short demonstration of another drill driver, to show what I was comparing the ones in this review against.

The product was provided by the store for review.