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)

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 power bank is a game-changer! It’s incredibly compact for a 40,000mAh capacity and easily fits in my pocket. The fast charging is legit—I got 22.5W on my Android and 20W on my iPhone, just like advertised. It charges my phone multiple times and still has juice left. The digital display is super handy for knowing exactly how much battery is left. Highly recommend!

I got this power bank for a backpacking trip to Havasupai. The power bank was great, exactly as advertised. It needed to be drained before I could charge it and I feel like I got so many charges out of it, it was almost hard to drain. The one thing I wasn't prepared for, but should have expected, was it did take about 12 hours to recharge it, so just account for that. Fast forward to our backpacking trip, we got hit with a flash flood. This power bank got me through multiple days, it was smashed into the dirt, got wet, still worked perfect and STILL wasn't even halfway drained by the time we left. Also, this was the lightest weight power bank I could find with 40000mAh and also pretty compact. Most others I tried were like bricks, but this one is great! Could not recommend more.

It's very compact and small and love it, charges really quick.

This product works well, tells you how much battery life is left. Sadly it does take some time to charge but still really good overall

Honestly I love this portable! It is a bit heavy but charges my stuff pretty fast. And I love that I can charge up to 3 things here. It holds up the battery charge pretty well I can go up to 3-4 days before needing to charge it again. I especially love the kickstand feature I can just simply watch something without having to hold my phone or prop it up, it can work vertical too if on a video call! Glossy finishes on the sides too.

I’ve always wanted a more powerful charger, but all of them are huge. Not this one! It’s small enough to fit easily in my Lululemon belt bag, and I’ve been able to charge my phone multiple times on one charge! This is now my go charger! If you are on the fence…just buy it…I promise you won’t regret it.

**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.