ZZI Portable Charger Pocket Size 40000mAh Power Bank,Fast Charging Battery Pack,USB-C Android-22.5W/iOS-20W Output,Portable Phone Charger Battery Bank for iPhone 16/15/14/13 Series, Samsung (Black)

My phone has a poor battery health. To get through the day I always need to charge my phone. I love that I can use it to on 4-5 different charges before it needs a recharge. I haven’t needed to use both ports at the same time yet but I have had one port stop working. I work on a construction site and dirt is everywhere. The port that stopped working is the one my cord is never plugged in to. So, I think it’s an environment issue and not an issue with the charger.

So far so good. It's bulkier than my last bank that was recalled, but has a higher capacity. It seems sturdy, turns on when you plug in and is easy to use. It comes with a shorty cable for charging a USB C phone or whatever. It takes a while to charge, at least off my phone's charger, but also charges my phone rapidly, faster than the last unit I had, and the battery in this lasts a lot longer. Overall happy with this purchase.PS, did not read the instructions, no clue what this slide out piece does 🤷‍♂️

this little compact lightweight charger holds a lot of juice, is small enough to keep in your pocket and quick to recharge.It is simple to operate and has all the features I need in a small portable charger. I hope you enjoy it as much as I do.

Works great, but its pretty big to have in your pocket. It will fit but its like having a very full and heavy wallet.

Nice day portable charger. Do wish it can be with little longer of a cord. Also, rather heavy but it lasts to charge my galaxy 23 at least 3 times.

I believe I looked at all of the chargers and this was the only pocket sized 40Kma charger available. Best yet, it was the least expensive of all the chargers down to 20Kma. The thing is tiny but it works very well.

Used about 6 times so far and it works well, as advertized

**Warning** Long and detailed explanation below!You may already know that there are a lot of games being played with mAh measurements on all battery packs. What most don't tell you is that mAh is a measure of current, not power or energy stored in the battery. Since all of the packs do it, it is useful for comparing between packs, but it also leads to a tendency to overstate capacity. Some packs are worse than others.You first need to understand that mAh is a meaningless number, unless you know the voltage. Typically, the Li-Ion batteries in these packs are about 3.7V. This particular pack has its actual numbers written on it: Pack Voltage = 3.85V and Pack Energy = 154Wh. This means the 40000mAh battery pack has a battery energy capacity of 40Ah*3.85V = 154Wh. Since USB runs at 5V (usually) this means the mAh capacity at 5V is theoretically only 30800mAh (148Wh/5V). The reality is you can't get 100% conversion efficiency changing the 3.7V to 5V. Some of that energy gets lost to heat in the batteries and conversion circuits. An excellent battery pack might be able to achieve 80% efficiency. A cheap, low end pack should be able at least 60% efficient. Anything below that is extremely poorly designed, in my opinion.I decided to test this pack with a USB power meter and a heated vest as soon as it arrived. This vest draws a little under 2A of power at 5V (about 9W). The pack started at 68% full (I like the digital capacity display!) I ran the vest until the battery bank reached 0 and shut down. It had output 9600 mAh at 5V which = 48Wh (9.6*5). Since the battery pack started 2/3 full, we can calculate what the 100% capacity would've been: 72Wh (48*3/2). This means the efficiency of power bank is 46.7% (72/154). Terrible! Or maybe the marketing is not telling the truth about the capacity or has limited the usable capacity to something lower to avoid over charging or undercharging the pack.To help determine which is the case, I the charged the bank fully with the power meter attached. This would show how much power is flowing into the power bank which would include the power being dissipated due to heat and efficiency loss. For example, if the batteries hold 154Wh of energy, it would take 184.8Wh of energy out of the wall charger to refill that 154Wh, assuming the battery pack voltage converters and battery heating effects create a 20% loss (154*(1+0.2)). Well, I refilled the entire bank with 84Wh of energy, nowhere close to the 154Wh expected. (See photo of the meter after charging from 0% to 100%) This tells me that the capacity claims of this battery are way, way off. Like, less than half as much as it should be.To be fair, I have tested another battery bank of the same rated capacity in the same price range and saw the exact same thing- a 49% overall efficiency. I have also tested a more expensive battery pack that is rated at 20000mAh that specified a 74Wh energy capacity. It is much closer to its rated spec and demonstrated a 73% overall efficiency. Thus, mAh ratings and power ratings for comparing battery packs don't tell the whole story.For the moment, I am still holding on to this pack, and may keep it rather than return it due to inaccurate advertising. At about twenty bucks, the price was OK for 72Wh of usable capacity. The size is nice for putting in the vest pocket and should be able to heat the vest for about 8 hours. The digital capacity gauge is nice. Build quality seems OK, except for a slide-out hook that I assume can be used to hang the pack from something. It is thin plastic and seems like it may break easily.Bottom line: I can't recommend this product due to the shenanigans they are playing with their ratings. I do give it a generous 3 stars because it does work, and 72Wh is still usable and OK at this price.Update: The seller contacted me about my review and offered a refund. They didn't ask me to change or take down my review in exchange, so that at least redeems them somewhat in my mind, though it doesn't address the usable capacity of this pack not matching the description.