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Harbor Freight Armstrong 2000 mAH Power Bank Review

Rating: five star rating

Harbor Freight Tools recently launched a new product line consisting of various chargers and battery-supplied power banks under the "Armstrong" name. One wonders if they got the joke*.

Today I'm going to be looking at the smallest power bank they sell, the 64977. This model is rated for a 2000 milliamp-hour capacity (or two amp-hours). As of this writing, I've seen this power bank offered in their stores for $5 and on their web site for $7.

Armstrong 64977 Power Bank
The actual product, or at least my example of it, lacks the "Armstrong" branding shown in the picture. Only the embossed "Power Bank" text is present. Beyond the power bank itself, you get a small USB cable to charge the bank. This cable can also power anything having a micro USB charging port. There's also a small instruction manual that doesn't tell you much, but does recommend that you turn the power bank off when not in use (it has no power switch), not use the power bank if you have a pacemaker (because having a pacemaker precludes owning, operating or even the thought of operating any electronic device), to have it repaired only by a qualified technician (not likely) and wraps things up by saying the power bank is only to be used "as intended". Oh, and it's not a toy either.

If you ask for the full rated capacity of the power bank all at once, you certainly won't get two amps out of it for an hour. There's always some inflation of the specifications as to much energy these things can deliver and for how long. In testing the power bank with a 500 mA dummy load, it managed to deliver about 1200 mAH before shutting off with an exhausted battery. Charging it showed about 1700 mAH worth of current going in over time, so I'd hazard a guess that the actual battery within has around 1500 mAH worth of capacity. Compared to the other power banks I have, the fib factor is no worse than any of them. Like most others, this bases on a lithium ion battery. There is a converter circuit within to boost the battery's voltage (from 3.7 to 5 volts or so) and to reduce the input voltage when the battery is being charged.

This power bank won't have capacity sufficient to bring most cellular phones back to a full charge, though it will certainly get you out of a tight spot if you've run out battery and need a little boost until the next time you can get to a charger.

The original USB specification calls for devices to receive 100mA worth of current without asking and up to 500 mA with permission from a host controller in a computer or similar device. Either one works out to pretty slow charging, and as far as I'm aware, no USB attached device makes such a request, nor does any USB host controller actually grant it. Most anything just takes what it wants, right up to the 500mA. A few "rude" devices just assume there's still more current available, and that they can just take it. More polite devices use a variety of different methods to ascertain whether more than 500mA worth of current is available from a given port, and to request that more power be made available for their needs. The result is a shorter charging time.

The Armstrong power bank fits into both categories. When charging, it drew nearly one amp from a laptop's USB port. This quickly tapered down to 750 mA or so and stayed around there until the very end of the charging cycle. Its output is coded to indicate support for Dedicated Charging Port, or DCP, functionality at up to 1.5 amps. Although the power bank is capable of delivering that much current, its connection points become quite warm in doing so and the internal battery won't manage it for long. Attached devices will get more out of it (albeit at a slower rate) if they limit their charging current to much less than the maximum.

Some approaches to high speed USB charging, such as Qualcomm's Quick Charge, also increase the voltage output when possible. This power bank does not support any of those methods. There is no means by which a device using USB-C can be attached. Most USB-C devices would also request a higher voltage output, and this power bank cannot provide that. (To my knowledge, Harbor Freight does not sell any charger or power bank that supports USB-C charging.)

For no more than it costs, and its comparable performance to other USB power banks of similar rating, this seems to be an entirely decent product. I've used mine several times so far, and while only time will tell, it has just done exactly what it was supposed to by providing a decent boost in battery capacity for a variety of different devices. I've even run a Raspberry Pi 4 from it for short periods of time.


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* The historical reference to an "Armstrong" battery as I had come to understand it had to do with early farm tractors (and cars) whose engines were started by hand-cranking them. Early tractors in particular oftentimes had no storage battery or electrical system beyond that needed to produce high voltage for ignition purposes. Thus, the joke about an "arm strong" battery providing the energy needed to spin the engine over and get it started. Perhaps the joke is less common than I expected or it has been largely forgotten. In preparing this review, I really expected to find some references to this elsewhere online, especially given the number of antique tractor and automobile forums. This demonstrates more of my boundless optimism, in spite of a strong belief driven by experience that Google searches are increasingly useless.