Vapcell U2 Universal Charger

I've wanted a simple, versatile device for my workshop for a long time. Then I happened to come across this one from Vapcell, got interested, ordered it for review, and today I can show you what it's all about.
Inspection, teardown, tests, conclusions.

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The price in the title is $13.39, but unfortunately shipping costs an extra $7.69, bringing the total to over $20 :(
But I think you could find it for quite a bit less by checking other stores or waiting for a sale. I'm just providing a link to the Vapcell store.

Why this charger caught my interest, and what its key features are:
1. It charges batteries up to 26 mm in diameter, though you can actually fit larger ones. A 32700 fits just fine, but it will partially block the second slot.
2. It supports batteries up to 75 mm long, so even protected 21700 cells will fit.
3. Supports all popular charging modes: Ni-Cd/Ni-MH, Li-Ion, Li-Ion HV, LiFePO4.
4. Charging current of 0.5/1 A with both slots occupied, or up to 2 A in a single slot.
5. Reverse-polarity protection, plus automatic recovery of protected batteries if their protection circuit has tripped.

It also supports power bank mode, though I personally have no use for it.

It comes in a small box listing all the key features, with an authenticity-check code as well.


The package is very basic: the charger, a USB cable, and a manual.


The USB-to-microUSB cable looks very cheap, and is about half a meter long.
The only really important information in the manual is the final charging voltage and current:
Li-Ion HV - 4.35 V, current 0.5, 1, and 2 A
LiFePO4 - 3.65 V, current 0.5, 1, and 2 A
Li-Ion - 4.20 V, current 0.5, 1, and 2 A
Ni-Cd/Ni-MH - 1.48 V, 0.5 A

Note that the charging current for Ni-Cd/Ni-MH is limited to 0.5 A. For the other modes, it's 0.5 or 1 A with both slots occupied, and up to 2 A with just one.


It looks like a standard two-slot charger. The only real difference from others is probably the layout of the buttons and indicators.


While preparing this review, I noticed that the slots aren't quite identical. The right-hand one is marked for use in power bank mode, rather than both slots, as you might expect.


The indicators use LEDs in different colors:
1. The three orange LEDs at the top show the charging current: 0.5, 1, and 2 A.
2. There are four LEDs on the sides: the two lower ones are blue, and the two upper ones are green. They indicate the battery type, then show the charge level at 25, 50, 75, and 100% once charging starts.
3. Two buttons at the bottom let you select the battery type and charging current.

By default, the device always starts in Li-Ion 4.2 V mode when a lithium battery is installed, and in Ni-Cd/Ni-MH mode when a nickel battery is installed.
My only real complaint is how it handles LiFePO4: the charger doesn't recognize them automatically, so after a restart it will try to charge them as regular lithium-ion batteries.

The LEDs aren't bright, which is great: they aren't annoying even when almost all of them are lit at once.


There are two connectors on the top end: a microUSB port for connecting the power supply, and a full-size USB port for connecting a load in power bank mode.
There are molded feet on the bottom, along with a repeat of the supported battery types and sizes.


The case consists of two halves held together by six self-tapping screws.


There's a single circuit board with all the charger's electronics. There's some flux residue here and there, but otherwise it looks decent. Some of the chip markings have been rubbed off, though.


1. As I understand it, the chip in the SO-16 package is a microcontroller. It's above and to the left of the converter transistor; the reverse-polarity protection circuit is on the right.
2. The other end of the board looks very similar, but there's another chip here. I assume it's some kind of operational amplifier.


There are just as many components on the other side of the board. This is where the power bank circuit is, along with the components for the charger's DC-DC converters.


1. Components near the USB ports.
2. Some transistors, apparently connected in parallel.


The moving contacts are spring-loaded, but the current doesn't flow through the springs. Instead, it passes through a metal guide along which the contact assembly slides.


I put it back together and move on to testing its main function: charging batteries.

First, a standard Li-Ion battery with a charge termination voltage of 4.2 V.
1–3. Charging at 0.5, 1 and 2 A. The actual current is a little lower, but the difference is most noticeable only at the maximum setting.
4. Charging stops at around 4.22 V, which is within the acceptable range.


The charger and batteries warming up while charging at 1 A also seems normal to me. The battery on the right finished charging a little later, so its temperature is higher in the last photo.


Charging LiFePO4 batteries.
This is partly why I needed a separate charger: even my S4 can't charge these batteries, and it's really inconvenient to get out the battery tester every time.

1–3. Charging at 0.5, 1 and 2 A is basically the same, which makes sense.
4. The specified charge termination voltage is 3.65 V. In reality it's a little higher, but given the steepness of the LiFePO4 charge/discharge curve, I can say this is absolutely not critical.


Temperature during charging. Here, too, it just so happened that the first battery was less discharged, so it finished charging a little earlier.
In any case, the temperature looks perfectly normal to me.


I don't think I have any high-voltage Li-Ion batteries, so I'll move on to nickel-based ones.
1–3. The only available charging current here is 0.5 A. Whatever value you set, it resets to 0.5 A anyway. But it uses a different algorithm: it charges for a few seconds, pauses for a second, presumably to take a measurement, then starts charging again.
As I understand it, charge termination here is based not on the voltage delta, but on the voltage when no charging current is flowing.
4. Unfortunately, I couldn't find out at what voltage charging would stop. Either my battery is dead or something else is going on, but the charger absolutely refused to switch off.


The current was low, though, and the battery barely warmed up.


After that, I discharged the battery for another experiment. When I later put it on charge and the charger switched off correctly, charging it to about 1.47–1.48 V, I decided to repeat the experiment—and I'm glad I did.
Maybe the battery had “woken up,” since it's already more than 15 years old, or maybe something else was going on, but this time charging stopped perfectly normally. The battery's maximum voltage during charging reached 1.57 V, not 1.7 V as before, and then charging stopped. Interestingly, even this old battery still has about 1100 mAh of its rated 1800 mAh capacity.


The description claimed reverse-polarity protection, and it really is there and works. That's standard for chargers like this, though; if one doesn't have this feature, it's a really lousy charger.


To measure the current at which charging would stop, I connected the charger to a battery tester, which essentially just monitored the current and voltage.
The one thing I hadn't accounted for was the tester's internal protection diode, which caused a voltage drop of about 0.4 V across the whole chain at 1.4 A.


You can see that the voltage is clearly below 4.2 V, and the current also decreased as charging progressed. Yes, I had set the current to 2 A here, and I can say that it drops toward the end of charging. It also depends on the connection in the USB ports and the quality of the power supply you're using.
In short, charging starts at 1.9 A, then drops to 1.3 A as the battery charges. After that comes the CV phase, and the charger switches off at a current of around 140–150 mA.

If you set the current to 1 A, it will hold steady throughout charging because that's below the 1.3 A threshold. To get a higher current at the end of charging, use a good USB cable or increase the supply voltage.


One more experiment, interesting in its own way. I connected a 0.1 Ω shunt and an oscilloscope in series with the battery. Basically, I needed to measure the charging current and see what was going on in this circuit.


I'll try to explain the problem. Sometimes charging is implemented like this: say you have a charger rated for 2 A, and lower current settings are achieved by changing its duty cycle. This isn't great for batteries with high internal resistance, because a steady 1 A is one thing, while 2 A delivered only 50% of the time is quite another.

1–3. That's roughly what happens here. In screenshots 1 and 2, the charging current is 0.5 and 1 A, and you can see peaks of 1.5–1.7 A. Only at a charging current of 2 A does everything look normal, with current peaks reaching 2.3 A, which is acceptable in principle.
4. This is a nickel battery charging. There are current spikes here too, but they're noticeably smaller than with Li-Ion batteries. At a charging current of 0.5 A, the peaks reached 1 A, rather than 1.5 A as in the previous test.


Charging a nickel battery; the pauses are clearly visible.


A few words about power bank mode.
It's very simple: it draws power from the battery in the right-hand slot, starts automatically, and switches to standby automatically when the load current is low or zero. Protocol support is extremely basic. It delivers its rated 1 A, but no more.
I don't see any point in running more extensive tests. It does what it claims, and that's all it needs to do.


As you can probably tell, this isn't my first charger of this kind. I'll tell you what I use and explain things in a little more detail.
First up is the one under review; there's not much to say about it here.
Second is the Nitecore, an extremely simple charger that works only with "regular" Li-Ion and nickel batteries, at a charging current of 0.5 A. One unusual feature is that it can run from either 12 V or mains power, thanks to a built-in power supply - review
My third charger served me faithfully for many years. Despite its simplicity, it's also a battery tester: it can not only charge at 0.5/1 A, but also discharge at 0.25 or 0.5 A while measuring capacity - review.
The fourth one is relatively new. It's not all that different from the previous one, but it has a higher charging current, a higher discharge current, and a few more features. Unfortunately, it still can't handle LiFePO4. Review.



Time to wrap things up.
This charger has both advantages and drawbacks, and one of the key drawbacks is its price. In this case, the price is what determines whether you can overlook the other issues.
On the plus side, it supports four battery types. The key feature for me is LiFePO4 support. It can charge at up to 2 A, but only when using a single slot, and it's easy to operate. Almost forgot: the slots are independent, so you can charge a nickel battery at 0.5 A in one slot and a LiFePO4 battery at 1 A in the other.
That's it for the positives. Now for the not-so-good. Yes, it supports four battery types, but in my opinion they could have added NiZn support instead of high-voltage lithium, since cylindrical high-voltage lithium batteries seem much less common.
Charging current and power input: why not add QC/PD support and allow 2 A per slot when both slots are occupied?
Third, at charging currents of 1 A, and especially 0.5 A, there are noticeable current spikes. This isn't good for charging batteries with high internal resistance. Unfortunately, this isn't a problem unique to this charger; it occurs with many chargers.
And fourth, if power is interrupted and then restored while charging a LiFePO4 battery, the charger will resume charging at 4.2 V, overcharging the battery. That said, rumors have it that only one charger can automatically detect LiFePO4.


In short, at this price, probably not. You'd be better off paying a little more for an S4 or the Opus. But if you can get the price down, it's a pretty decent charger. At around $10, I think it would be a good deal.

That's all. I hope you found this useful.