Power-Bank-Portable-Charger - 40000mAh Power Bank QC 4.0 and PD 30W Quick Charging Built-in LED Display 2 USB 1Type-C Output Compatible with Most Electronic Devices on The Market(Dull Black)

Assuming a valid computation of the power bank's capacity based on how long it takes to charge some device is erroneous. Different power banks have different charging circuits which can substantially invalidate the computation. And for using discharge-time to calculate how much power bank capacity is used to charge a phone, different power banks may vary many10s-of-millivolts, which will vary the time to charge the phone enough to make this assumption invalid.A better way to test a power bank's capacity is to get a "USB tester." They're surprisingly inexpensive, and they all have accurate calculators that display how much charge(mA-hrs) is delivered to a device (or power bank) under charge, including the total capacity when charge is completed. It occurs to me that it would be accurate to tally up the milliamp-hours going into a phone's battery by turning off the phone while it's charging, so the tester will only be tallying up battery-capacity, without the phone using up any charging current. Of course, for measuring the capacity of a power bank, you don't have to worry about charge going anyplace besides the battery.If you want to determine the total capacity of, let's say, a power bank, Step 1 is to discharge the power bank all the way. Discharging the power bank completely is not a nice thing to do to its lithium battery, so I try not to do that test, myself. But if I ever do the test, I'll update here with a result.In practice, I like keeping one of these monster power banks near my seat, if I don't have an AC USB charger nearby. And I like the bank's small digital display of remaining percentage to tell me that the power bank needs to be recharged before it gets over-discharged. And, just to make trouble, if the percentage readout were off by a few percent, the display is still sufficient to help avoid over-discharging the power bank so if achieves long life (and prospers). Instructions say to recharge the power bank before it drops below 25%. I would add "... if you have the chance."To treat my cellphone batteries most gently, I like to charge them most slowly (if I'm not going anywhere, such as during bedtime). A USB tester will tell you if a quick-charge method is increasing the charge-voltage above 5 volts, which may be quicker, but that's not the healthiest way, generating heat inside the battery, etc. I must remember that the power bank's USB-C jack is not only an input for charging the power bank, but it also can be used as an output to charge a device, for a total of 3 outputs from this power bank(!). I'll have to get my USB tester to confirm the USB-C jack is a plain, no-quick-charge output.

It was at the bottom of a drawer, among old cables and manuals for things I no longer own. Black. Unbranded. I don’t remember buying it. I’m not even sure it’s mine.I slipped it into my bag without thinking. I didn’t use it during the trip. Outlets were everywhere. Nothing seemed to justify its presence. But I didn’t take it out.One night, in a room with curtains that didn’t fully close, I woke up without reason. Outside, a streetlight filtered in like a thought that refuses to leave. I turned on my phone. Everything was fine. Still, I plugged it in.It lit up. A small point of light. I couldn’t tell you what color. I watched it for a few seconds, then unplugged it and went back to sleep.Since then, I always carry it with me.Not because it’s useful.But because that night, something —tiny, quiet— felt aligned.And sometimes, that’s enough.

This is easily one of the best portable chargers I’ve ever purchased. It can recharge an iPhone multiple times and has never let us down. One of the most impressive things is how long it holds a charge. I put it away for the winter and when summer rolled around, it still had 100% battery after months of sitting unused.It also recharges quickly, so you can top it off right before a trip and be confident it’s ready to go. It’s not too bulky either and feels solid and comfortable to carry around.

Seems heavy to use for travel. Takes a long time to charge. Built for durability. Bright flashlight.

Love this charger. It is pretty heavy to carry in a purse but fully charges my phone at least twice. Easy to use quality product. Has lighted indicator so you know what % is left on it. I’m ready for emergencies at all times by keeping it fully charged. Also has a flashlight.

Long story short, when testing this out it has potentially only 1/4 the capacity that they advertise. See below for the details.My iPhone 14 Pro Max has a battery capacity of 4,323mAh. This power bank supposedly has a 40000mAh capacity, which is the reason I bought it. Being able to charge my phone nearly 10 times off this thing could come in incredibly handy in an emergency.So I bought this a few months ago and tested it out and while the math didn't seem to add up, I knew I'd still get a couple full phone charges out of it so I didn't bother complaining, as I didn't have any other power block and it was certainly still useful.A few days ago I decided to get another power block with a bit higher wattage, even if it was rated a smaller battery (25800mAh). Today I tested the two of them together.Both power blocks were topped off at 100%. I used an app to drain my iPhone battery down to 80% and then plugged in one of the blocks and charged it to 100%, then did the same for the other block. I compared the time it took to charge the phone from 80% to 100% and how much juice was left on the power block afterwards. I closed out all my apps and had the same functions off/on, same brightness on my phone etc. and didn't use my phone at all during the tests. Here are the results:-"40000mAh", 30W power block (the product you're looking at): Took about 85 mins to charge my iPhone 14 Pro Max from 80% to 100%, and had 92% left in the block down from 100%. That means you'd use up about 40% of the power block charging my phone one time from 0% to 100%.-25800mAh, 65W power block (the competitor): Also took about 85 minutes to charge my phone from 80% to 100%, and had 91% left on the block down from 100%.Summary: The charge time was the same on both, and was done with a USB-A to lightning cable. My phone's battery, again, is only 4,323mAh. So in a perfect environment (which I'm aware this wasn't) charging 20% of that capacity means 864.6mAh was used, which brought the power block to 92%. That means the capacity on this power block you're considering would be around 10808mAh, or roughly 1/4 what it's advertised as. The other power block which is advertised as just over half the capacity of this one was nearly identical in power usage (1% off). The competitor still didn't add up to the advertised 25800mAh it had, but of course there may be other factors at play that impacted both tests (maybe the last "20%" of a phone charge uses a disproportionate amount of power, my phone was still on and technically using power as it was charging, etc.)Even if you don't trust my admittedly barely scientific math in this quick test (which is understandable), the fact remains that a power bank advertised as 40000mAh only actually has roughly the same capacity as another power bank advertised as 25800mAh.Now, the other power block I got is valued at twice as much as this one, so in that respect this is still a value. In the end the price is still good on this product, just make sure you're ok with not having anywhere near the advertised capacity. My star rating reflects the suspected false advertising of capacity from the seller.**updated review**Add not being able to survive one 3 ft drop to the review. I accidentally dropped this off my desk, and now it’s rattling and nothing you plug into any of the ports charges.