Features of off-grid power, or what to do during rolling blackouts, Part 1: power banks

Lately, I’ve been asked the same question several times: how to keep various devices and appliances running during a power outage. Today I wanted to talk a little about this so I don’t have to repeat the same answers in private messages, and can save myself some time while giving you more complete answers.

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After repeated attacks on Ukraine’s infrastructure, particularly power plants and distribution substations, we’ve recently been dealing with problems with the power supply. For some reason, Russian propaganda presents these attacks as a fight against the Ukrainian Armed Forces, which seems a little... strange, because soldiers out in the field with their own power supply couldn’t care less. Meanwhile, ordinary civilians are the ones who suffer: some people simply can’t cook a meal for themselves and their child because they have an electric stove at home; others can’t use the elevator and have to haul a stroller up and down the stairs. Yet the Ministry of Defense briefings say things like, “We hit another Tesla factory in Kharkiv with precision weapons” (not a joke—I didn’t know before that we apparently have a Tesla factory that makes electric cars).

Anyway, the problem exists, and we have to find some way to deal with it. I had to do that back in the late 1990s and early 2000s, when we also had rolling blackouts. In the end, that prompted us to develop and manufacture our own UPS units, though I was working with a business partner at the time. Who knew that more than 20 years later I’d have to recall all the details and quirks we ran into back then?

So, this article draws in part on what I learned back then, but takes into account today’s realities: both the nature of the problem and the new technologies and devices available.

Let’s start with power banks, the most accessible and almost self-contained class of devices. “Almost” because they still need a power adapter (or, as people commonly call it, a charger). Other than that, it’s simple: buy a little box and use it.
Simple, but not that simple, as it turns out there are all sorts of quirks and details. I’ll try to organize them somehow.

1. Capacity.
It seems straightforward, but even here buyers can be misled. Most often, you’ll see labels on power banks like 5000, 10000, 20000, 40000 mAh. These figures refer to the capacity of the battery inside the power bank, expressed at a voltage of 3.6–3.7 V. So even if it contains two 5000 mAh batteries connected in series, the label will say 10000, even though technically it’s 5000 mAh at 7.4 V. Maybe that’s even simpler.


But sometimes even a little one like this can come in handy. I think it’s useful to keep one in your bag: it’s light and small, but can really save the day.



But that’s the battery capacity. You’ll get less at the output because of physics: the power bank boosts the output voltage, so you won’t get the full 5000 mAh listed on the label. And there are losses too—in other words, efficiency.

Roughly speaking, the power bank converts the battery’s 3.7 V to 5 V at the output, so we’ll get at most 3.7/5 = 0.74 of the original capacity. That means 7400 mAh from a power bank rated at 10000 mAh. Taking efficiency into account (it varies between models; let’s say 90%), that’s 7400 × 0.9 = 6660 mAh—almost half the advertised figure.

But don’t worry: apart from the efficiency losses, the rest of the energy hasn’t gone anywhere—you’ll get all of it, just at a different voltage. And when power banks with other output voltages (9, 12, 20 V) appeared, it became clear that it’s much easier to calculate capacity in watt-hours rather than amp-hours.
A 10000 mAh power bank has a capacity of 37000 mWh, or 37 Wh. In other words, it can theoretically power a 3.7 W load for 10 hours, or a 37 W load for 1 hour.

In this case, whatever we do with the voltage, the energy delivered hardly changes, so it’s much easier to calculate.
Manufacturers are gradually moving toward listing not only the battery capacity, but also the capacity available at different voltages, as well as the battery capacity in Wh—which is more accurate and convenient.


But let’s get back to the capacity figures users are more familiar with. Power banks rated at 5000–10000 mAh are convenient as portable devices that you can toss into a purse or pocket to charge your smartphone or tablet. I especially liked a power bank in the form factor of a 21700 battery: compact and versatile.

Next come higher-capacity power banks, rated at 20000–40000 mAh, and sometimes even 60000 mAh. They usually offer much more: first, they often have multiple outputs, but the key point is that they can not only charge a device, but also power it for quite a while during an outage. They’re much less convenient as portable devices, since you can usually charge one on a train or in a car. A bus trip is a bit trickier, but it’s unlikely you’ll be riding a bus for that long. Well, maybe someone will take one hiking, although every gram is precious even there.
Keep in mind that if you plan to fly, there are limits on the capacity of your power bank's battery:
a power bank's capacity must not exceed 100 Wh; power banks with a capacity from 100 Wh to 160 Wh are allowed, but no more than two per person; if a power bank is over 160 Wh, you won't be allowed to take it on board.

Recently, power stations with very large battery capacities and lots of outputs have become popular, but their high price is holding back wider adoption.


2. Port types.
This part is quite straightforward; these are the options you usually see.
For charging the power bank itself:
microUSB - low charging power, only up to 10-12 W. This is a serious drawback for high-capacity power banks: for example, a 40000 model will take about 20 hours to charge through this port.
Apple Lightning - roughly the same specs as microUSB.
USB Type-C - a more modern connector that is more convenient to use and allows charging at up to 100 W (more powerful versions are already available, but are still uncommon). In theory, our 40000 mAh power bank could charge from it in an hour and a half. You have to admit, 20 hours versus 1.5—or even 2—is a substantial difference. But it depends on the power bank and the power supply.

For connecting devices:
USB Type-A - better known as regular or old USB. Older power bank models provide up to 5 V at 2-3 A (some versions go up to 5 A, but require a special connector) and up to 20 V (though more often up to 12 V), with power up to 18 W.
USB Type-C - the same as for charging: up to 20 V at 5 A, i.e. up to 100 W.


Sometimes a power bank may have a 5521 or 5525 socket, or simply a "round socket," most often for charging from a regular 12 V power supply or a car cigarette lighter, but there aren't many devices like this. It may also be a 12 V output, but those are even rarer.


3. Output voltage and current options.
Older models typically provide something like 5 V at up to 2-2.5 A, enough to charge any smartphone or almost any tablet, but charging can take a long time because the power is low.
Newer models support the Quick Charge or QC protocol, which can charge faster because the power is no longer 10 W, but up to 18 W. More importantly, it puts fewer demands on the cable, since losses are lower at a higher voltage for the same power.
Even newer devices support the Power Delivery protocol, with power up to 65 W, or up to 100 W when using a special cable. As I mentioned earlier, more powerful versions exist too, but they're almost never available for sale. Output voltage can reach 20 V, with current up to 5 A, making these power banks suitable not just for smartphones and tablets, but also for laptops. A Type-C connector is required.


There are also proprietary protocols and modes, such as Samsung and Huawei. The latter's voltage and current differ noticeably from the more common standards.


4. Type of batteries used.
As we know, a power bank isn't just a little box that magically produces electricity. It has batteries inside, and they come in different types.
Most often, you'll come across power banks with flat batteries; these power banks are flat themselves. These batteries often offer a pretty good capacity-to-volume ratio and a shape that works well in a power bank.


But nothing comes for free, and experience has shown that these batteries are more prone to swelling. By the way, batteries of this type are used in your smartphones and tablets, and sometimes in modern laptops too. This problem doesn't affect everyone, but there have been cases, and it's worth mentioning. These batteries are also less mechanically robust, although that's really a problem with the power bank's design. Power banks come in both metal and plastic cases.


The second type is cylindrical cells, most often in the 18650 size. I'd say they're a more reliable and sensible choice, if it weren't for a trick used by Chinese manufacturers. If your power bank has cells from a reputable brand (LG, Samsung, Murata, Sanyo), you can rest easy: they'll most likely last a long time. But sometimes manufacturers use cells of unknown origin, and you end up with not only lower capacity at the same size and weight, but also a shorter service life.


Power banks designed for easy battery replacement are also available. They're convenient not only because you can swap out cells as they run down, but also because they can work simply as a charger. I've even reviewed a couple of models like these.


There are also DIY kits that use cylindrical batteries, usually 18650 or 21700 cells.


There are also more "budget options" where you buy the case and use your own batteries. I've reviewed one of those, too.


The main thing at this stage is not to start cobbling together something downright crazy from whatever happens to be lying around. Sure, with the right approach, even that can work, but keep in mind that if one of the batteries short-circuits, you'll get a "boom" in your home. Is that really what you want?


5. Cables, triggers, and adapters.
Regular USB cables are mostly much the same, except that some are made much cheaper and have only the power wires. These cables may not work properly with modern devices, and charging will be slow because the data lines are also used to let the charger (power supply) tell your device what current and voltage to charge at. If that information isn't available, the device charges much more slowly.
Type-C cables are in some ways more complicated and in others simpler. With almost all such cables (meaning cables with a Type-C plug at both ends), your devices can charge at up to 65 W. If a cable has Type-C on one end and regular USB on the other, it works like a regular USB cable.
But there are special Type-C cables with a dedicated chip inside that lets a device draw up to 100 W (20 V, 5 A), provided the power supply supports it, of course. In other words, to get 100 W, all three devices must support this mode: the power supply (power bank), the cable, and your tablet, laptop, or smartphone.


This cable, on the other hand, looks pretty dubious, because you can't get 20 V at 5 A—that is, 100 W—from a regular USB port, since it doesn't support the Power Delivery protocol.


If your laptop doesn't support this type of charging (having this kind of port doesn't necessarily mean it does; check the manual), you can buy a special adapter with a chip inside that tells the power supply (power bank) to output a specific voltage. The adapter usually has a Type-C cable socket on one end and a plug matching your laptop on the other.


There are also cables that combine the cable itself, a chip, and a plug that fits your laptop, but the selection is much smaller.


The subject of power banks is actually much broader, but I think I've gone on long enough. So, here's the bottom line: what do we have, and what do you need to know to choose a power bank?
First, decide what you need it for:
For occasional top-ups of your smartphone—like a spare tire in your car, just enough to get you to the repair shop—a 5000–10000 mAh model will do. Fast charging isn't essential; it's easier to wait. These models are cheap, lightweight, and compact.
If you use your smartphone or tablet a lot and sometimes spend a long time away from an outlet, get a larger model, say 20000 mAh or more. Fast-charging protocols are often included, but not always, so check whether you actually need them.
If you have a work laptop as well as a smartphone, look for models with a capacity of 40000 mAh or more, and make sure they support the Power Delivery protocol (PD 2.0, PD 3.0). You'll also need an adapter for powering your laptop and a compatible cable. I also recommend checking whether the power bank supports fast charging; otherwise, you'll be waiting a loooong time for a battery this large to charge.

I'll wrap up part one here. In part two, I plan to talk about how UPS units work, calculating battery capacity and choosing a battery for long runtimes, along with a few other details—if anyone's interested, of course.
And if you have any questions about power banks, let me know and I'll add to the article.