Reviewed in the United States on January 7, 2020
1) Can jump start a car?
2) 5V output line is fairly well regulated, stays around 4.8V at the 2A load. With this 2A draw, it runs for over 5 hours on full charge. This is good enough to recharge your phone 2-3 times, and juice up a laptop with compatible input for an extra 2-4 hours.
3) Nice features: two USB smart ports with up to 12V output, USB-C charging and output, red-on-black functional display,
1) The supposed 12V output is actually 16.8V at full charge - both at the clamps and at the barrel jack (see the photo). The output is not regulated at all: under load (in my test case, 1A), it steadily drops from 16V to just under 12V, when fully discharged. This basically means that internally they simply rout 4 lithium cells in series to both so-called "12V" outputs, without any regulation circuitry in between. When the cells are fully charged, it gives 4 x 4.2V = 16.6V, when fully discharged it becomes 4 x 3.15V = 12.6V (actual voltage will drop obviously under load, especially past half charge). Applying voltage this high to a car’s 12V charging / lighting circuit is probably ok, meaning that it should be pretty tolerant to voltage swings to begin with, but does have a potential to fry some stuff, say interior light bulbs. Same goes for your 12V gadgets: you could use it, hoping they can withstand the 16V actual, but you shouldn’t.
2) Overstated capacity. Again, running this with a steady load of 2A on the 5V output (4.8V actual average), the unit produced 10690mAh, before shutting off. I consider this a representative test as that’s what most people’s phone would use. This comes out to 51.3Wh, or assuming a 3.2V nominal cell, 16000mAh total capacity. I.e. nowhere near the advertised "21000mAh power bank". In fact, assuming a lower discharge rate (fudging really), it would come closer to 16800mAh - which is consistent with most similar units on Amazon, where sellers do not engage in creative marketing.
3) Wireless charging is a useless gimmick. I.e. if you are out in the wild and happen to have this thing with you, why won’t you simply plug in the charging cable? This way, you will waste less energy, recharge faster, and at least be able to make a phone call.
4) Cranking amps. Considering the actual capacity of about 16Ah and a rule of thumb that a lithium cell safe discharge rate is around 4C (i.e. 4x capacity), this unit can safely put out around 64A, which really isn’t enough to jump start a regular car. Very high quality cells can withstand up to 25x draw for a few seconds, which brings the cranking amps into a 400A range - which is consistent with the claim that it will produce 500 cranking amps for 3 seconds. 2000 amps? I don’t think so. Perhaps, the "auto-boost" clamps do have some kind of circuitry capable of transcending the physics of lithium batteries for a few seconds, but I have no way of verifying that.
Among many lithium-based, compact jump starters available on Amazon that also double as power banks and share many features and specs (including the over inflated capacities and capabilities), this BeatIt G18 seems to have the most compelling feature set and a better implementation of those. Compared for instance with the very similar DBPower G15, it has 2 smart USB ports vs 1 and and a functional display, which I take any day over blue dots or bars. Speaking of the G18’s display, it’s a red-on-black LCD, a nice thought - easy to see in the dark and daylight, without a need for a backlight. As a newer generation design, the unit also comes with a USB-C charge port that can be used for the output as well (though, depending on the packaging, a USB-C wall charger may or may not be included).
On the other hand, if you really like the idea of having a portable power bank, and jump-starting a car is only a secondary consideration, then there are better alternatives available. The DBPower DJS50 turned out the best I could find: not only it has a very well regulated 12V output, you can also select 16V and 19V - in addition to the two requisite USB 5V outputs. It also comes with a collection of attachments to plug in any regular laptop (you’d need an adapter for Macbooks). To top it off, it also has a higher actual capacity (in fact, pretty darn close to the advertised 18Ah or 57Wh). It also has a blinking red light, a nice-to-have for emergency signaling. After all that, it's priced $30 lower, likely because it’s considered a previous gen unit.
Getting back to this G18. It might be a fair jump starter (within reason), but falls a little short as a power bank, on two counts: over inflated capacity and unregulated 12V output. If you understand the limitations, it should serve fine. Hence the 3 stars.
Last, but not least: the company behind this brand is engaging in feedback solicitation, i.e. buyers are enticed to freebies for posting positive reviews - an unfortunate, but all-to-common practice nowadays. In all likelihood, the thousands of positive reviews here are meaningless. However irksome, it's probably no different from what's going on with similar products.