Inside a new style eBay tool battery - with schematic 

I really just wish I was smart enough to fully appreciate these videos

The 13-page Chinese full datasheet on page 11 shows a full reference design, including those series resistors on the pins. The good stuff is always in the Chinese datasheet...

I like the way the brand of the battery on the thumbnail is kaboom

3:41 "I roughly know what I'm gonna see inside. Air, mainly." It reminds me of the time Dr Ashens took apart a cheap clone games console and discovered that the manufacturers had put a big metal weight in the case to make it feel heavier and classier!

The "prominent brand names" do make good money on their batteries, but what goes in also costs more. Big difference is that the big-name batteries are going to have cells of known providence with very precisely defined characteristics that will meet or exceed the rated values (seriously, a lot of the off-brand stuff is made from whatever cells are cheapest on the spot market, and the spot market has a huge problem with fakes and uprating). The casing tends to be a significantly better polymer, the internals have things like insulating sheets and thermal fuses, the bus bars are significantly larger in cross-section, and the quality of the battery terminal welds is vastly better. There also tends to be a lot more expense on things like load testing, lifecycle testing, drop testing, and so on. I use tools from one of the Prominent Brands pretty much daily, and have a mix of real and knockoff (half the price) batteries; the knockoffs are fine for things that don't put a huge demand on the battery (radio, worklight, etc), but they just die horribly if I try to use them in a high-draw tool (looking at you, angle grinder...). Meanwhile, the real batteries chug right along. Also, the off-brand ones tend to have a much shorter lifespan, as measured in number of recharge cycles.. The real ones will usually last about 18 months of regular use, while the knockoffs, despite not getting worked nearly as hard, often don't make it a full year before it becomes glaringly obvious that they aren't holding anything approaching a full charge. (And we're not getting into the industrial-sector tools, like Hilti, where they have a product line where the battery stores diagnostic information for the tool and uploads it to the charger during the normal charge cycle so that tool managers can identify and replace tools before the guy using it on the assembly line is aware of the problem.)

The strap on the B3 terminal is VERY close as well! They could have put a strip of fish paper under the battery terminal that crosses the copper.... that would cushion the clip and helped with possible shorting.

As someone who as done 2 years of Li-Ion battery pack manufacturing, those welds are not only abhorrent in strength and quality (They just full sent a popped weld on the bottom right, which essentially only has a *half* weld holding it on!) just by visual inspection, a single weld is poor practice. Industry standard is 2 sets minimum. I bet with just a single drop from arm height the welds will shear. The nickel is also probably plated steel which is a bad idea for high drain tool batteries, though in this particular case it's probably okay since the little saw won't draw too much. That's all not even mentioning the elephant in the room of relying on solder mask as insulation between cells! That was the craziest part to me.

Clive seems to be doing a lot of chainsaw stuff lately. Should the locals be worried ?

Reaches for the Kapton tape and begins fidgeting. Thanks for sharing, it is educational and entertaining as always.

Damn, the spot welding is another point of failure and a possible fire or explosion 😱

With this, and the chainsaw videos, can I request a spin off series, similar to the ‘Will It Carbonate’ called ‘Will it Dismember’ whereby Clive tries to cut through various items with the cheap (slightly dangerous) hand chainsaw. Start simple with items like twigs and branches, then move on to more exciting things like frozen joints of meat, lithium cells, Ralfys flat cap etc.

The battery midpoint taps should always be designed to effectively be "fused" as near to the cells as possible. Major brands accomplish this by either using thin wires , highly narrowed down nickel strip, or SMD resistors on a flexible pcb mounted over the cell ends. The fact that these guys pulled full width nickel (steel?) strips for midpoint-voltage-sense right up to the BMS PCB is a flagrant violation of battery safety 101 ! It's these kind of fouls that causes most of the battery fires and thus the new laws showing up that prevents us from having ebikes indoors in major cities.

As a hobbyist I have skirted round electronics for years now. Mains projects are doubly trebly quadruply safe, no reg is left unexamined. It is like painting-with-numbers, I am very good at doing stuff, but haven’t a clue what’s going on. Actually, that describes my life.

That's why brand is a fact. I have been using a "Total" brand cordless impact drill from 2020. No issues at all. Last January, 2024 both of the batteries just died while drilling. When I checked I found out that 1 cell from each pack went to 0v. So I just replace the cells with Panasonic ones and now it is all fine. But the main thing is, it is well built. They have none of the problems shown here. PCB traces are good, nickel strips are well designed specific for the battery pack. A good product actually.

I bought a cheap whipper snipper and it came with 2 similar batteries. No matter how dodgy they are built, actual fires are rare. Thanks for the great reverse engineering.

Hello Clive, Can you make a video about the LIDL batteries and chargers? They have a 20 V and a 12 Volt battery line. All the batteries use 4.2 V 2 Ah 18650 cells. The 20 V 4 Ah battery costs 25 pounds and has a 2P5S configuration, and the Battery Management circuit also provide cell balancing. Nowhere in the instructions says that for cell balancing to work, the battery must be left in the charger for several hours after the charge had ended. Thank you Anthony

“Yes, there was a bit of a spark… ✨ _exciting_ ✨” God, I love Clive. 😄

0:25 That's interesting. The lube pump is commonly seen as a petrol primer bulb on garden tools.

I like the 'over-zooming' as I tend to watch your explorations on my phone. With a cup of tea. First thing in the morning, in bed.

Thanks for sharing your knowledge and time!

This is why I tend to open up these kinds of batteries. To inspect them, and to fix dodgy assembly work. I'd rather not use that one, as is. Depending on how hard it is to open them up, I might also add a balancing connector and RC-style power connector, so I can charge them with a balancing charger, every now and then. If the pack is easy to open, I just add temporary balancing leads whenever I feel like rebalancing the pack.

standing by to see the wart filled with air. I could tell in the vid it was light as a feather

Oooh, 21 volts; one more volt than normal! That's probably what they were hoping people would think.

I really enjoy your videos sir, especially ones about battery packs, thank you!

Hi Clive, Brilliant video as usual. One thing about these "21v" batteries, is that they are not actually 21v, Thy all have 5 cells in which is exactly the same as the 18v batteries from branded names. Even fully charged they do not supply 21v. The circuitry doe not boost the battery output. There are hundreds of cheap Chinese tools with these batteries all purporting to be 21v. I actually purchased a drill and when I found the batteries were not as described I requested the correct ones from the seller. After many Emails, no 21v battery was forthcoming and a full refund was given and they did not require a return.. Keep up the good work Clive.

My dewalt packs were failing and I found replacement cases on Shoppee that come with nickel strips and bms just add quality lithium ion batts. Got one that holds 15 cells and another that holds 10 21700 cells. Back in business!

This kind of battery is from small factorys. They do not have design team and just buy case, battery, pcb from other factory and assembly.

Enjoyed your explanation on operation of batterypack.

I’ve always had a sneaking suspicion that the markups on Makita/DeWalt/prominent tool brands are entirely arbitrary. I sincerely doubt that the circuitry, and the manufacture costs, would warrant a 50-80 pound price to make any profit. Stuff like this is a bit of a confirmation for me, I think.

After hearing about all these lithium battery fires, I have a lot more respect for well designed chargers! Cheers..

All praise design errors! It's the one thing keeping Big Clive in business!

All resistors are fuses, in a way. As seen in MacBooks, were the actual fuses are the least likely to blow.

Nice to see Big Clive doing reviews of low-budget _elemental_ technology now... 😁 🌬 The tool is as light as *Air,* 🌎 The charger has no *Earth,* 🌊 The product was as cheap as *Water,* and 🔥 Need I say more about the battery? 😉

I'm glad you covered this battery pack as I was considering buying one of these hand chainsaws, that missing charge terminal would indicate that they were considering making the pack Makita compatible as there are other versions on Ebay what claim the packs are Makita charger compatible.

oh my, that looks very exciting!

funny timing, i JUST got some genertic lithium ions battery packs from goodwill that i plan to re-build some nicad tools with

Ah what a treat. I bought a frankly brutal garden strimmer the other day that use these very batteries

Best channel on YT.

oooh I like this chainsaw tool. The oil pump is a big plus.

Same battery i used with a fan. Great for high fan flow during hot days and it last 3-4 hrs low power.

"air, mainly" 🤣

Nice shout out to another channel I watch as well clive being "project farm" 😊

Leaving out the NTC just boils my blood. I think an SMD NTC is less than a 3 cents in 1000 pcs. Talk about penny pinching!

Interesting, the noname strimmer my mother bought has two of those batteries included. It was the first time i saw those battery packs with a barrel jack to charge it.

That unpopulated terminal is used by Makita to check the temperature. It should be at or slightly below the full battery voltage. I built a few batteries on my own using these kinds of BMSes and Makita tools don't work with them since that pin doesn't have the right voltage. What I've done was to disconnect all the traces from that terminal and short it to the positive. The Chinese have basically repurposed that terminal for charging. I've even seen some knockoff Makita chargers that have only that pin connected and they don't actually work with real Makita batteries, only with these types. Also because of the female jack terminal these batteries don't fit on original Makita chargers because of the yellow terminal.

I have a similar mini chainsaw, got it about a month ago. It works well, there is a thermal trip strapped onto the motor to detect if that is getting too hot. I am now going to check the battery and alter if that strap is too close to that track. DO I add a thermistor, well I think I will.

Getting slightly better but still not fantastic safety measures. The track issue's you pointed out Tab B2 also looks very close to B1. Solder resist is not much use as an insulator. interesting look into how to charge batteries 2x👍 I had to tidy up my area after a technical goodness "(e-waste)" landslide 🤣🤣

Thank you, keep working.

The lead out of the charger is Copper Coated Aluminium and in my experience, insulation spit, twist and short to FUThiss. One of my China tools is a 1/2 inch (with 1/4 inch hex drive in the centre) impact driver and it is a superb tool that takes huge punishment. For an ebay cost of £35. Batteries working well but the charger is the weakest link.

I have a couple knockoff Ryobi batteries. They have spring clip tabs on the sides. Most, if not all of them, don’t have any insulation between the ends of the cells and the large metal springs. If you manage to press the spring in too far, it’ll short out two cells. The springs are held in place so that won’t be a problem, right? Oh, wow. The springs are held in place by pieces of tape. About as robust as masking tape. I open them up when I get them and add kaptan style tape, and epoxy to hold the tabs in place. The nice thing about Ryobi batteries is that they have built in MOSFET low voltage protection. So I can connect them to random circuits and not worry about draining them too far.

Got a really neat cordless hydraulic cable crimper of AliExpress, cost about £400 in all. It came with makita clone batteries but I got an adapter to use it with my dewalt batteries! It came with 2x 5ah batteries and I'll probably use the 18650s out of the for something else, I was pleasantly surprised by the build quality of them though..

Thanks for sharing. 😉👌🏻

I work for a Heritage Railway and we use a lot of cordless power tools and they have come a long way, where we could use a power tool for only two or three hours max and the battery is flat and now the power tools have more power and we can use the power tool for four to some times five hours before they need to be recharge but these are the upmarket tools and cost £ 160.00 up to!

Isn't it not "just" the whole battery pack that has been placed wrongly (a couple of mm too low). I supose that the battery taps should cover the hole area with all the smsll through holes. All the other taps are also misaligned

It is further development knock off 18V Makita battery, @ 2:42 this odd missing connector is needed on Makita tools. On those it has to be connected to +, it signals to tool that battery is OK. So this is "inspired" by Makita but no longer can be charged or used with Makita tools/chargers. This missing pin is used on Makita chargers for charging aswell (atleast on slow 3A chargers).

oof.. that design just asks to explode, with it relying only on the insulation of the solder mask..

Ah, that makes me leery. I believe the negative was what scorched on my cheapie (untrusted, fortunately) Amazon pack. In this one that would've been potentially very unfortunate. On mine it just meant a quick trip to the parts bin.

These battery packs do make me slightly nervous , I kinda wish all the cells had thermistors on them but im guessing that would push up the design/price, Im also wondering would it be worth fitting a balance cable to these things to rebalance them from a pro hobby charger?

I’ve found with almost all those mini chainsaws that the trigger is designed to be pushed with the middle finger. Try it, and you’ll see that there is a notch (or choil) for the forefinger in front of the trigger. Don’t know if that’s good or bad, but they are easier to hold if you use it that way.

Pleasantly surprised they didn't cost cut the hell out of that protection circuit. Would have been good to have the NTC, but a single string of batteries isn't likely to get THAT hot in most cases. Pity about the layout. Maybe in the next version? 👍

Be interesting to see inside a Milwarkee battery with all the smart data stuff.

Great shooting Clive:” Fingers And The Brains

Those chinese battery chargers are basically regulated supply with an op-amp checking if the voltage has reached the wanted voltage, and they often come overvoltaged and kill cells, at least in my experience

I bought a small chain saw and a line trimmer one came with the same battery as these but the one that came with the chainsaw has a battery voltage test button other wise the same batteries

Hard to tell for sure, but it looks like the B3 tab is really close to the B1 pad. Not as bad as the other you mentioned, but closer than I'd like.

1:25 - on the left hand side, terminal B1 and B3 look to have the same dependence on the solder mask serving as insulation.

is the thermistor not wirebased and mounted from the backside. the parallel resistor can also serve as a linearisation (even though the value in that case likely would not be 10k)

I once had an unbranded power bank fail catastrophically in my backpack because the positive battery contact was laying across a ground plane with only soldermask separating the two. It did, eventually, blow the track clear, but not before melting through the case and producing tons of smoke. When I pulled the smoking power bank out of my bag, I could see the battery wire glowing red hot through a hole melted in the case. With the number of overlaps in that tool battery pack you have, I would be very nervous about it myself.

"I accidentally triggered that. It was quite interesting." Another Clive understatement?

I do not like that B2 tab sitting on top of the B- solder mask either. I guess it's time to take your snips and trin it back a bit. Maybe you could slide a thin piece of plastic "from packaging" in-between the metal clips to add some protection there as well. I just ordered a $29 dollar version of the mini chain saw from amazon in the USA. I will be checking out the 2 batteries it comes with for sure. Thank you for the tear down and heads up.

B3 connection tab also has the same problem as the B2 connection tab. Might be that the tab width has changed after the PCB design since the tabs looks like they are unusually wide.

The big brands like DeWalt, Milwaukee, Makita and so on definitely make an absolute killing whenever some poor sod buys a single battery or two. I had to buy a single 18V 5Ah Milwaukee battery years ago and it was about £150 at the time, keep that price in mind because a year or two later I bought a battery/charger combo. Six 5Ah 18V batteries with a charger that could take them all at once, for about £350. You get the same thing with those package deals where they sell you a sawzall and a drill with batteries, a charger AND a "free" M12 battery thrown in just so they hook you on that front as well, typically a pack like that is also around £3-400. The markup is absolutely ridiculous.

When would they use the third big mosfet pad by the big mosfets?

Your camera is really great. It's almost unnecessary to do the zoom picture now. My parents' biggest fear when I was a young child was which electronic device would be disassembled next when they weren't looking hahaha.

looks similarly close on the other side, i'd run a bit of superglue in those gaps to act as a bit of an insulator!

Looking forward to diy air purifier!

3:30 I recently bought some power tool off Ali and the first thing I noticed when I took the charger out of the box that it is _unrealistically_ lightweight! They must have found the way to produce antigravity and this charger must contain _loads_ of it 😅 Can't wait the video to see actually what is inside! Don't make me wait for too long for it! Just one moment, please! 🤣

My partner bought an unknown brand compact chainsaw that came with a couple of these battaries. Ir runs for a couple of minutes and then the chainsaw acts like battery is running flat, going slow and then stopping completely. Leave it for a little while and it's fine for a couple of mins again. Suspected some protection kicking in somewhere (either heat or power draw related) which is a shame as others have used similar tools and found them really good, which is why they suggested them to her. She has bought another compact chainsaw now and will see if that is any better. I was shocked when I picked up the charger unit as it's so light I was expecting it to be empty and a fake charger, but does actually seem to charge the battery somehow. Will be interesting to see your strip down of the charger.

Do you, by any chance have an actual Makita (or equivalent brand) Battery pack for comparison? It would be quite interesting to see what shortcuts the cheapy packs take and how that impacts safety.

I discovered that 18v Makita tools with "Star Protection" won't work with these packs as is, on these generic BMS boards, C+ contact has to be jumpered to the main positive and voila, angle grinder works. Not sure if it's good for the bms tho.

Hey Big Clive, please can you do a video on the 2 types of Ryobi batteries circuitry protection etc. In South Africa we get a completely different tool and battery and feels cheaper than what's available in UK. Our tool colour and battery system is completely different.

finally chainsaw with actual safety interlock. imagine falling and grabbing it... my ryobi mains one has that. and it also had automatic oiler instead of manual hope yolo oiler. it's implemented by solenoid in series with motor. restricts it's usage angle tho

One thing I've noticed on eBay, locally at least, is that the vendors (all Chinese, of course), don't sell these batteries separately. Not even if you want to buy a new replacement pack. No idea why. But they do sell the circuit boards.

I just left a comment on your other chainsaw video about the cut off switch. I think your old broken chainsaw has a cut off switch on the handguard if it is like a normal chainsaw.

Good to see one with oil

I agree their is not enough clearance between those two contacts

I ALWAYS open up "impossibly cheap" products containing high energy density batteries, to find and fix anything dangerous.

It would be good to see a genuine makita lxt video, see if they are that much better.

It's interesting how the Chinese play the "battery voltage inflation" game. Makita would call this battery an 18V one; Dewalt might call it a 20V one, but this manufacturer goes whole hog and calls it 21V. After initial discharge, the battery voltage should settle to 18V.

I have one of these handheld chainsaw things, looks about the same, and mine has failed - turns on for like a second after pressing the button and no more. I tested the battery when pressing the trigger and it has proper voltage, drops under load a few volts but ok. I'm suspecting the potted electronics that drive the motor then :( (checked the switch and with another battery too)

I would be interested to see what it did on a Makita charger. Since the real ones do have balancing which would make it last much longer.

They have per cell connections, presumably for low voltage detection, but don't do any balancing?

You could carefully cut the overhang off the tab with a dremel to open the clearance maybe.

Clive, there's a handheld fan popular in Asia which has battery management you might find interesting. Search SAPI N15b portable fan and you'll see some images. It has no low voltage protection but uses the digital percentage 'meter' to cut power when it counts down to zero. I tested the two 18650 parallel cells at just 937 mAH combined and replaced with batts with cells totalling closer to 5000 mAH. There's charge protection to 4.2v but when the meter counts down to zero the fan shuts off with higher capacity batts still reading 4.0v. Unexpected 🤦

Thanks :)

I like the [ Robbie the robot ? ] oil squeezer , for some reason ( ? ) ............... DAVE™🛑

Is spot welding battery tabs directly to PCB pads a good idea? I think that’s the first time I see it done like that. I don’t think the risk of lifting a trace is high, given the today’s generally decent PCB manufacturing standards, but don’t they run a risk of corrosion caused by a high current running through small surface interface area between two dissimilar metals? Unless that’s exactly the point: a smart self-destruct timer, of course 😉

I wonder how many of these batteries explode during manufacture due to the potential for shorts in several places on the circuit-board?

I would have thought the inter-cell connections are also used for cell balancing... Wouldn't the 1k resistors reduce that ability dramatically?

Do you know about 2-cell (series) bms chip with balancing? Most chips I found only do monitoring (HY2120-CB, S-8242A) and stops charging when first battery reaches 4.2V. Something really simple to implement and small.