The item listed shows a cell phone size device that is 50,000mah. If the size is accurate that would be 4 18650 batteries. At 2,500mah that would be 10,000mah. That means that 40,000mah is missing.
At 2,500mah, an accurate size would need to hold 20 18,650 batteries.
Keep the form factor of what you are buying, in mind, and see IF the mAh matching the advertised storage.
My general advice: never believe the advertised capacity of any kind of battery. Especially when the manufacturer is anonymous to avoid false advertisement penalties, lawsuits, and the like.
Addendum: don’t buy chintzy battery-powered junk on ebay
According to eBay, 18650s are up to something like 9000mAh now - generally from brands with names ending in -fire that are best avoided. Funny that Panasonic made cutting-edge cells for Tesla about 2 years ago that were optimistically 3600mAh; 3400mAh is best you can reliably find in the wild from Panasonic, Sony, LG, Samsung.
Li-Poly can overcome some of its density shortcomings vs Li-ion by being more space-efficient since it can be made into arbitrary shapes, so that could account for some powerbanks with decent capacity and inconvenient dimensions for 18650s. But a large segment of consumers want “the most amp-hours for the dollar”, so the most absurd claims will win with uninformed buyers.
@Diplomat, that picture doesn’t show scale. That pack could be much larger than the anticipated cell phone size. All I can tell from the picture is that it is rectangular and at a price point that suggests too good to be true. Also, there are flat gum stick profile LiPo batteries, I youst to import them from china, some of their capacities can seem surprisingly high until you figure out the volume compared to a 18650 and find out they have quite a bit more volume.
I warn about the size as I recently purchased a Larger battery pack and expected an item half the size based on the picture and other battery packs I had seen in person.
This was a reminder to look at the size vs the mAh rating to see if the form factor was reasonable for the mAh. The same measure can be said about the price to mAh.
The catch is you can’t tell the size from your picture, there is nothing in the picture that shows scale. In this case the price point is the more telling feature. That being said, price point isn’t always telling as you might be buying a returned item that was auctioned off in bulk from a reseller. I’m currently trying to buy ego 7.5 Ah 56v battery packs at pennies on the dollar. Grabbing one of these msrp $340 batteries at $60 sounded way too good to be true, but it was due to it coming from returned items auctioned as not working when they were actually just fine.
Without dimensions it’s all just speculation, but perhaps we can indulge in some informed speculation.
The shape is reminiscent of a package that’s commonly used for Anker 11 and 13AH packs, sized roughly for 4x 18650 (2750 and 3250mAH, respectively)
There’s a 7-digit display on one end - unless the thing is significantly larger than normal and the unit is something like the size of an enormous hardcover book it’s closer to roughly phone sized
Glancing at the apparent listing, I came across the dimensions for the even better-er 80000mAH pack:
I doubt that’s even 8 amp-hours, to say nothing of 80.