USB 21700 Charger Genuine IMREN4600-USB Rechargeable 3.7V Battery, 100% Real 4600mAh High Capacity(2 PCS)

Update on the size: On my digital caliper, I measured 76mm with the button top and 75mm without the button top. And such a length may indeed be too long for some devices as I one of my lights didn't work with it (along with another 76mm battery of different brand). However some devices like the Coast WPH34R headlamp and Coast XPH34R headlamp can use the battery and the Coast XPH34R actually *requires* the longer 75/76mm battery. The stock Coast ZX955 battery is also 76mm long.Addressing the other reviewers complaints about the size: first, the product description in a big image explicitly shows the width to be 21.5 mm and the length to be 75 mm. Second, lithium cell size format is only nominal value, and not an absolute size spec. I can't speak for vapes, but most devices use spring tension to account for differences in lengths. The width can be slightly larger due to wrapping and the length varies with protection chip, button top, and charging port each adding to the length. So unprotected flat top cells are the shortest, while protected button top cells with charging port are the longest.For the capacity, I used two devices to test:- XTAR VC4SL which appears to discharge to < 3.5V but above 3.0V: this resulted in 4466 mAh- Vapcell S4 Plus, which discharges to the batteries' cutoff voltage if protected, or 2.5V: this resulted in 5025 maHSo the stated capacity is indeed accurate, a rarity for a lot LiOn batteries here.I don't have a way to measure maximum discharging current, but it does work in powering my high powered flashlights at max brightness e.g. 3800 real lumens. The specs and battery label itself does state a continuous current of 8 amps (power: 29.6 W @ 3.7v and 33.6 W @ 4.2v), which should plenty to sustain most devices IMO. I assume peak non-continuous would be quite a bit higher, maybe 50% to 100% more current.

The Amazon description clearly says "built-in integrated safety circuit protects battery from over-charge, over-discharge, short-circuit and over-heat," yet the back of the packaging (which is conveniently omitted from any of the product photos) says: "Do not discharge at below 2.75V or charge at above 2.4V... Do not disassemble, cut crush, incinerate or short-circuit the battery." This warning is present on the power cell as well, and is of course also omitted from the product photos.So does it have built-in short circuit, charge, and discharge protection or doesn't it? One of these sets of statements is a lie, and I'm not going to give them the benefit of the doubt.Upon further inspection, the "Safety Tips" section at the very bottom of the Amazon page also says "Never short-circuit... Never use on any devices without protective mechanism... Never over-charge or over-discharge."It appears that the sellers of this product are deliberately lying about its safety features. Li-ion power cells are not toys and can violently self destruct if not properly managed with appropriate circuitry that this seller claims is present. I purchased this item instead of a standard 21700 SPECIFICALLY because I wanted built-in protection circuitry. Otherwise it's just a naked power cell with a USB socket.

These have a good capacity as claimed, but the button tops get really hot while charging

Love being able to charge with a built in charger

The battery works great. I'd give it 5 stars.But not everything needs to come in a plastic case. Its a battery. Its going to live in my flashlight, not in a case. The only reason this came in a plastic case was so they could pretend they used very little packaging material because "that's not packing, its a case". Stop it!

Happy to get this 4600mAh 21700 button top type for my flashlight.

I love the idea, but it's too long to be a 21700... A 21700 battery is 21mm x 70mm, this is closer to 21mm x 76mm, so it just won't fit my device. I returned it. But, if it had fit my device, I'd have kept it because it's super cool.

Very tight in my equipment.