Taking Apart a USB-Rechargeable Nickel-Zinc AA Battery: Useful, but Only for Users Who Know What They're Doing
イチケン / ICHIKEN
The electronics YouTuber Ichiken came across a battery chemistry they had rarely heard discussed: nickel-zinc. The sample is an AA-format cell sold by MAKERZ, which Ichiken describes as a Keyence group company that sells mechanical and control-related parts and small electrical items. They note that it is unusual for a Japanese company to sell this kind of product, which more often shows up as Chinese gadgetry. Over the video, Ichiken checks the specifications, takes the battery apart, measures its performance, and concludes that it works well as a battery but is not a straightforward substitute for ordinary cells.
The Specifications and How They Compare
The cell is labeled Zn-Ni. Ichiken points out that, unlike lithium-ion batteries, nickel-zinc batteries do not use a flammable electrolyte. The rated figures are a nominal voltage of 1.6 V and a nominal capacity of 1200 mAh. The official page says the capacity varies between individual units, with a guaranteed minimum of 1080 mAh.
On paper, that capacity is lower than Panasonic's eneloop nickel-metal hydride (NiMH) battery, which is rated at 2000 mAh. Ichiken cautions that milliamp-hours can mislead here. Nickel-zinc and NiMH cells run at very different voltages, so the fair comparison is energy in watt-hours, which they measure later. The rated cycle life is 500 or more recharges, against more than 600 for eneloop. Ichiken considers 500 cycles fairly standard.
The battery carries no PSE mark, unlike products that use lithium-ion cells. According to Ichiken, nickel-zinc batteries, like NiMH batteries, do not currently appear to be regulated items. They are unsure whether that will change but guess it probably will not.
The Built-In USB Charger and Its Trade-Offs
The main selling point of the MAKERZ product is a charger built into the battery. Charging starts as soon as you plug in a USB cable. Ichiken says they are not a fan of this design and explains why.
Easy charging is convenient. However, the charger takes up space inside the AA shell, which leaves less room for the cell and therefore reduces capacity. For that reason, Ichiken says, the built-in-charger design is at a capacity disadvantage compared with plain nickel-zinc cells sold without one.
Charging is also slow. The manual gives 9–10 hours, and Ichiken says it really does take that long. They compare this with roughly two hours for quick-charging NiMH batteries and call 10 hours too long. Ordinary NiMH chargers also cannot be used in its place. The battery voltage is too high, so such a charger would conclude that the battery is already full or that it is broken.
Weight and Open-Circuit Voltage
The battery weighs 21.2 g. For comparison, Ichiken measured the eneloop at 26.9 g and an alkaline cell at 24.7 g, so the nickel-zinc battery is a few grams lighter. Ichiken attributes this to the charging-circuit section inside, which is low in density compared with a battery cell.
Freshly charged, the open-circuit voltage measures 1.85 V. For reference, a charged NiMH battery reads 1.40 V. Ichiken notes that its nominal voltage is 1.2 V, and that rechargeable batteries generally read above their nominal voltage right after charging. An alkaline battery reads 1.54 V.
Under load, the MAKERZ battery holds around 1.6 V. Since alkaline cells sit around 1.5 V, Ichiken considers it an easy voltage for replacing alkalines. They see it as especially suited to high-power loads that would normally run on alkaline batteries, and they explain the reasoning later in the video.
The same high voltage becomes a drawback in devices designed around NiMH cells. Ichiken says the voltage would be too high in that case, which does not look good. This is where they first state their main verdict: the battery is basically for people who know what they are doing, and people who don't should not use it.
Disassembly: What's Inside
The battery says not to take it apart, and Ichiken disassembles it anyway. It separates into three parts:
- the battery cell;
- the charging-circuit section at one end;
- a sleeve that connects the charging circuit to the cell.
Opening the charging section reveals the positive-terminal projection, some black cushion-like parts, and a small circuit board. The board uses very small components and appears to contain only two ICs.
Ichiken traces the circuit. The 5 V USB input passes through a diode that prevents backflow, which Ichiken approves of. The charging is based on an LDO regulator. There is no inductor, so the circuit does not use switching conversion. A section of control circuitry sits alongside.
The key finding is that the cell's positive and negative terminals are routed straight out to the battery's external terminals. Ichiken describes the product as an ordinary rechargeable cell with a charging circuit attached in parallel. As a result, the built-in charger is optional. If you apply voltage directly to the external terminals, you are connected to the cell, and Ichiken shows that the battery can be recharged this way.
The Protection Claims That Couldn't Be Confirmed
The sales page lists overload, short-circuit, and overvoltage protection. Ichiken argues that the circuit layout makes this impossible, because the cell terminals connect directly to the outside with nothing in between.
Their experiments matched that reading. They drew about 10 A from the battery. They were unsure whether 10 A counts as overload for a cell this size, but no protection kicked in. When they charged the battery at a high voltage from an external source, no overvoltage protection intervened either. In their testing, Ichiken could not confirm that any of the three advertised protections worked, and they believe the battery simply does not have them.
Ichiken does not see the missing protection itself as a flaw, since other rechargeable batteries lack it too. What they object to is advertising a function that does not exist as though it does.
Discharge Curve, Capacity, and Energy
Ichiken measured the discharge characteristics at 0.2C, a rate often used in testing standards, and plotted voltage over time alongside a NiMH battery for reference. The nickel-zinc battery ran at a higher voltage throughout. It started at 1.85 V and stayed around 1.6 V during use. Ichiken reads that sustained high voltage as high power.
At 0.2C, a battery that delivers its rated capacity should last five hours. The MAKERZ battery reached full discharge in about 4 hours 45 minutes. Its measured capacity was 1146 mAh, below the 1200 mAh nominal figure but above the 1080 mAh minimum, so Ichiken places it within the range of unit-to-unit variation.
Ichiken expects many viewers to see the mAh figure and conclude the battery is weak, so they also measured energy, which they consider a better guide to how much a battery actually holds. MAKERZ does not publish a nominal Wh rating. The measured figure was 1841 mWh, which Ichiken calls about what they expected and less than the eneloop. They attribute the gap again to the built-in charging circuit shrinking the cell.
Internal Resistance
Both batteries had internal resistance in the tens of milliohms, with the MAKERZ cell somewhat higher at 80 mΩ. Ichiken explains the difference with the construction: the cell terminals are brought out through lead wires, a printed circuit board, and solder joints, and the measurement includes their resistance. They add that users can only use the battery in its assembled form, so 80 mΩ is the effective performance of the product.
Noise: A Clear Advantage Over Lithium-Ion AAs
Ichiken has previously reviewed USB-rechargeable lithium-ion AA batteries, and those had a noise problem. They step 4.2 V lithium-ion cell voltage down to about 1.5 V with a conversion circuit, and that circuit generates noise.
The MAKERZ battery has no voltage conversion stage, because the cell terminals are simply brought out. Its noise is therefore very low. Ichiken demonstrates this with a radio. On the nickel-zinc battery, the background noise between stations is minimal. On a lithium-ion AA battery, the background noise is loud. Ichiken concludes that this battery should work even in noise-sensitive equipment like radios.
Self-Discharge
Ichiken did not measure the self-discharge of the cell itself. They did measure the current drawn by the charging circuit that sits in parallel with the cell, and it was under 1 nA, essentially zero. They calculate that a continuous 1 nA draw for a full year would equal about 0.0007% of the battery's capacity. The charging circuit's contribution to discharge is therefore negligible. Ichiken expects the cell's own self-discharge to matter more, though they note they have not checked it.
Can It Replace Alkaline or NiMH Batteries?
Ichiken says many viewers probably want to know whether nickel-zinc batteries can replace alkaline or NiMH cells. Their view differs by device type:
- Devices designed for alkaline batteries: probably fine.
- Devices designed for NiMH batteries: battery voltages vary quite a bit, so Ichiken cannot say for sure. They think it will probably work more often than not. Their advice is still clear: if you are not sure it will work, do not make the swap.
Ichiken believes the bigger practical problem is usually not the voltage during operation but what happens when the battery is nearly empty. A discharged nickel-zinc battery still reads about 1.5 V at the cell. A device reading that voltage is likely to conclude that charge remains.
Ichiken describes the likely result. The battery is actually empty, so its voltage drops as soon as the device starts drawing current, and the device stops. After a rest, the voltage recovers, the device again sees apparent charge, runs briefly, and then fails again. Ichiken finds this easy to imagine happening repeatedly. They expect that some users would decide their device was broken and contact the equipment manufacturer.
Verdict
Using the MAKERZ product as an example, Ichiken concludes that high voltage and high power are the main strengths of nickel-zinc batteries, and that the chemistry genuinely suits applications that need them. The MAKERZ battery has a built-in charging circuit, but the cell's output reaches the terminals directly, just as in a conventional battery, and it works fine as a battery. Because its voltage is higher than that of ordinary batteries, however, Ichiken considers it a product meant for people who know what they are doing.
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Hello. Today, I found a battery I hadn't heard much about, called a nickel-zinc battery. I will disassemble and review it. Here it is. It's a nickel-zinc battery from a brand called MAKERZ. I'm sure many of you know this: MAKERZ is a Keyence group company. It's where they sell mechanical and control-related parts and electrical accessories. It is quite rare to find a Japanese company selling products like these Chinese gadgets. What is a nickel-zinc battery? We will check it while disassembling. But first, here is today's sponsor.
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First, let's check the specs. It says Zn-Ni: nickel-zinc batteries. A characteristic of nickel-zinc batteries is that, unlike lithium-ion batteries, no flammable electrolyte is used. One feature is that they don't burn. Nominal voltage is 1.6 V. Nominal capacity is 1200 mAh. According to the official page, nominal capacity varies due to individual differences in the product. It appears to be at least 1080 mAh.
For a different type of battery, Panasonic eneloop, a nickel-metal hydride battery, is 2000 mAh. By comparison, the nominal capacity is less. But with nickel-zinc and nickel-metal hydride batteries, the battery voltage itself is completely different. To see the energy of the battery, we need to see capacity in Wh. We'll examine this later.
As for the number of recharges, it is more than 500 times. For reference, the number of times eneloop can be recharged is over 600 times. I thought 500 recharging cycles was standard.
Looking at the entire battery, unlike products using lithium-ion batteries, no PSE mark is indicated. Nickel-zinc batteries, like nickel-metal hydride batteries, currently do not appear to be a regulated item. I'm not sure if they will ever be in the future; probably not.
A feature of this battery is that it has a built-in charger. Just plug in the USB cable to start charging. However, I'm not a fan of the built-in charger. It has advantages and disadvantages. First, it's good to be able to charge easily just by plugging in the cable. Conversely, the volume of the built-in charger means a smaller battery cell size, and as a result, the battery capacity will be lower. Therefore, capacity is at a disadvantage compared to nickel-zinc batteries sold as individual battery cells.
By the way, recharging the battery takes an awful lot of time. The manual says 9–10 hours. It really does take this long. Considering that quick recharging of nickel-metal hydride batteries takes about two hours, 10 hours is too long. Also, chargers used for nickel-metal hydride batteries cannot be used interchangeably. The battery voltage is too high, so the charger would detect that the battery is already fully charged or that it is broken.
From here, we will measure the performance of the battery. First, the weight: 21.2 g. For reference, the nickel-metal hydride battery eneloop is 26.9 g. An alkaline battery is 24.7 g. Thus, compared to other batteries, it seems to be a few grams lighter. I know why it's so light: because it has a low-density charging circuit inside.
Next, we measure the open-circuit voltage. Fully charged, it is 1.85 V. It is a nickel-zinc battery, so the open-circuit voltage is high. For reference, a nickel-metal hydride battery is 1.40 V. Its nominal voltage is 1.2 V, but when these rechargeable batteries are charged, generally the voltage is higher than the nominal voltage. And an alkaline battery is 1.54 V.
As you can see, nickel-zinc batteries have a high battery voltage. They seem to be suited for high-power applications, especially as replacements for batteries used for high-power loads that run on alkaline batteries. I'll explain more about why later. The voltage of the MAKERZ battery during discharge is about 1.6 V. In contrast, as we saw earlier, the open-circuit voltage of an alkaline battery is about 1.5 V. Therefore, it is a convenient voltage for replacement.
On the other hand, if you use this battery in a device that is supposed to run on NiMH batteries, the voltage would be too high. That doesn't look too good. Therefore, this is basically a battery for people who know what they're doing. If you don't know better, you shouldn't use it.
We will disassemble it from here. It does say not to take it apart. I'll disassemble it anyway. When disassembled, it is divided into three parts as shown here. Here is the battery cell. This one on the far left is the battery charging circuit. In the middle is a sleeve for connecting the charging circuit and the battery itself.
Further disassembly of the charging circuit part gives us this. This is the projection of the positive terminal. In addition, this can be removed like this. These black parts are made of a cushion-like material. And here is the charging circuit. The circuit is built with very small components. There appear to be only two IC components. Various parts have been omitted.
The circuit is shown here. Here is the 5 V input, and the terminals on the right side are the positive and negative battery terminals. This part is the battery cell inside, and this part is the battery charging circuit and so on. Let's start with the USB input. A diode is in place to prevent reverse current. Good. The charging circuit is based on an LDO regulator. You can see it in this circuit. Components such as inductors are not used inside, so switching-based circuits are not used. And here, it contains circuits for various controls.
The terminals of the battery cell are brought directly outside. The positive and negative of the battery are brought outside as they are. For this part, the specifications are the same as other rechargeable and dry cell batteries. Think of it as a circuit for charging attached in parallel to the battery.
As you can see from this circuit, when charging, you don't actually have to use this charging circuit. If voltage is applied directly to the battery terminals from an external source, they are connected to the battery inside, so it can be recharged. When the battery is actually connected, it can be recharged like this.
The sales page also lists overload, short-circuit, and overvoltage protection. This circuit configuration cannot provide that, because the cell terminals are brought directly outside. In an actual experiment, it can carry about 10 A as a load. I'm not sure whether 10 A counts as an overload for this battery size, but no particular protection activated. Also, even if you apply a high voltage externally, it can be recharged without overvoltage protection activating. As far as I've experimented, I could not confirm the operation of overload, short-circuit, or overvoltage protection.
Not having this kind of protection is the same as other rechargeable batteries, so from Ichiken's point of view, that's not a problem. I think it's a problem to describe a function that doesn't exist as if it does.
Here is a more detailed look at the performance. First, discharge characteristics were measured. Here is the graph. The discharge rate of the battery was set at 0.2C, which is often used in testing standards. The horizontal axis is the time elapsed since the start of discharge, and the vertical axis is battery voltage. NiMH batteries are placed on the same graph for reference.
The results show that nickel-zinc batteries have a high overall voltage. The open-circuit voltage is 1.85 V, and the voltage continues to be maintained at about 1.6 V during operation. It continues to produce this high voltage, which means high power. If it can keep discharging for five hours, that would mean it has the rated capacity. It took about four hours and 45 minutes to fully discharge.
From the test results of these discharge characteristics, battery capacity was also measured. Eneloop is also shown for reference. For nominal capacity in Ah, the MAKERZ battery is 1200 mAh. The actual measured capacity is 1146 mAh. Since this product is said to have at least 1080 mAh, although it is less than the nominal capacity, it is within the range of individual product differences.
Looking at this table, I'm sure many people think the capacity in Ah looks small. Looking at Wh makes the amount of energy in the battery easier to understand. Measurements were taken for that as well. The nominal capacity in Wh is not disclosed, so that is left blank. The measured capacity is 1841 mWh. I guess that's about what I'd expect. The capacity in Wh is less than eneloop and so on. In the case of MAKERZ, it has a built-in charging circuit, which makes the battery cell smaller, and that has an effect.
Now we also measure the internal resistance. Both have internal resistance as low as tens of mΩ. MAKERZ's is a little higher, at 80 mΩ. We know the reason for this. Inside, the battery cell terminals are connected through lead wires, printed circuit boards, and soldering points. The resistance in that area is included in this. But from a battery user's point of view, it can only be used in this state. The internal resistance of 80 mΩ is the performance of this battery.
Next, we will look at the noise the battery makes. Previously, when we reviewed lithium-ion AA batteries that can be charged with USB, noise coming from the voltage conversion circuit was a problem. This noise comes from the circuit that converts the lithium-ion battery's 4.2 V to 1.5 V, which is the voltage of an AA battery. This MAKERZ battery does not include a voltage conversion circuit for its output. The battery cell terminals are brought directly outside, so noise is very low.
You can actually try it on the radio. This is the noise sound. There is very little background noise when not tuned in. For lithium-ion AA batteries, this is the noise sound. There is a lot of background noise! Even for equipment like this, where noise is a problem, these batteries seem to work.
I'll check self-discharge next. I'm measuring with this kind of circuit. It doesn't tell us about self-discharge of the battery itself, but the current consumption of the charging circuit attached in parallel can be measured. How much current does it actually consume? About this much. It's less than 1 nA, almost zero. Suppose 1 nA is consumed continuously for one year. This corresponds to 0.0007% of the battery capacity. Therefore, battery discharge due to this charging circuit is almost negligible. I haven't checked, but I think cell self-discharge is more significant.
Finally, can alkaline and nickel-metal hydride batteries be replaced with these nickel-zinc batteries? I know many of you are curious about this. What is Ichiken's view on this? For equipment designed to run on alkaline batteries, maybe it's okay. For equipment designed to run on nickel-metal hydride batteries, the battery voltages vary quite a bit, so I can't say for sure. I think it's probably going to be okay more often than not. But if you're not sure it will work, don't replace it.
From Ichiken's point of view, in many cases the practical problem will be when the battery level is near zero, rather than the voltage during operation. Here is a discharged nickel-zinc battery. If you look at the cell voltage, there is still about 1.5 V. Even when the battery is used up, the battery voltage is still high. Equipment may recognize that there is still battery power remaining, and operation may become unstable.
What does that mean? Since the battery level is zero, as soon as you start using it, the voltage drops and it will not work. If left for a while, the voltage will recover. From the equipment's side, it appears to have battery power remaining, so it works for a very short time, but the voltage drops again soon and it becomes unusable. It's easy to imagine this happening. If this happens repeatedly, I expect a certain number of people will mistake the equipment containing the battery for being broken and contact the equipment manufacturer.
So, I've disassembled and reviewed a product offered by MAKERZ as an example of what nickel-zinc batteries are like. The high voltage and high power are the main selling points, and I think nickel-zinc batteries are a good fit for such applications. MAKERZ's product has a built-in charging circuit, but the cell output is brought directly outside, as with conventional batteries. It works fine as a battery. However, the voltage is higher than normal batteries, so we think it's basically a product for people who know what they're doing.
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