KunHe USB Rechargeable AA Batteries (4 Count) Double A 1.5V 1200 mAh USB AA Rechargeable Battery 4 Pack

These reusable batteries are a game changer. I like to just have them pre-charged so I can have them ready for use. It is easy to charge, and the instructions are easy to follow. You just take off the top and plug it into a USB charger spot (such as a the laptop or a portable charger).Reusable batteries are the way to go.Note: it does not work if you directly plug it into an AC adapter.

I got these batteries about 6 months ago. Haven't charged them more than 20 times and already I have one that won't take a charge. Last time I charged it the green light stayed on even after I took it off the charger.Then it lost all power over night. Now it won't charge at all. They are slightly inexpensive but not cheap.I expected more for what I paid. Definitely won't get this kind again.

So I'll start off by saying that these have definitely come in handy , the convenience of being able to just take the cap off and plug in anywhere to charge is a life saver . I use these for gaming,the kids toys decorative lights and my RC hobby , the charge speed is pretty great doesn't take too long for a full charge(will update on time ) , my only issue with these are that in some cases the positive contact post is too short for some items but for the most part they works great . Compact and ready to go with a overall great build quality, I've dropped these a few times while out driving my RCs and they've never failed me . Lastly unlike most other brands it's definitely worth your money especially way better than the other disposable ones.

Fast charging

All four batteries would not charge. I tried several USB A ports on two different laptops and a desktop with no success. I even tried the various charging blocks we have for other electronics. Nothing worked, so my only conclusion is that the entire pack was defective from the factory. I've returned them and will be looking for other options.

I ordered these because I wanted to have a way to make sure I always had fresh batteries for my wireless controllers, with the cost of batteries going up, and controllers using them faster. I wanted to get out of the circle of using batteries and changing them out and having to purchase new ones. with these barites I am able to put freshly charged batteries in my controllers and charge the dead ones by using my pc or car charger anything that has a USB port. allowing me to not have to store bulk batterie purchases and hope that they will all hold the charge until i get to use them. so far they are lasting longer than store bought AAs and completely charge in under 2 hours.I hope this helps make your decision easier!!

I came back and bought another pack of them just because I love them so much for my older electronics without rechargeable batteries. We would have killed for these back in the gameboy days. Don't have to dig out a bespoke charger, just plug them into a USB and wait for them to stop flashing. I'd recommend a cheap USB hub just so you can do them all at once, as they do take up a bit of space and can be hard to get situated next to each other if you have to charge more than one at once. I find they last a perfectly adequate amount of time in game controllers, computer mice, and even milk frothers.I'd love to see how long these actually last in terms of how many recharges they can handle, but for the price it's an absolute steal even if I do have to replace them a couple years down the line.

The USB-rechargable AA-size 1.5V lithium batteries seem intriguing, so when this brand broke under $10, I tried them out. So will this type of battery take over from alkalines and NiMH? The short story: they are useful, but the capacity is low and the control circuit is too easy to fry - use only cheap chargers! Also, the USB plug part is shorter than standard, it does not fit well in some USB sockets. Similar, more expensive, products from other brands may, or may not, be better, as they face the same design challenges.To understand the "capacity" of devices like this, one must realize that watt-hours (energy) is what matters, not amp-hours. The device - like USB "power banks" - converts 5V input into about 3.7V in the battery. And then converts again for output, in this case to 1.5V. When the voltage is converted, so is the current. E.g., if a current of 100 mA is drawn out of the 1.5V output, i.e., a power of 150 mW (100 mA * 1.5V), the 3.7V lithium battery needs to supply a current of about 40 mA (150 mW / 3.7V). Actually the conversion is not 100% efficient, so probably about 50 mA. If the capacity of the actual battery is, e.g., 500 mAH, then that will continue for up to 10 hours (500 mAH /50 mA). At the 1.5V output, that translates to 10 hours times 100 mA = 1000 mAH.So what is the actual capacity of this battery? I tried to measure it by attaching an iMax B6 charger in discharge mode. For an unknown reason, that instantly fried the control circuit inside this little battery, causing it to discharge itself in a hurry, lighting the LED and making the area around it quite hot to the touch. I put it on a rock outdoors in cool weather (in case it explodes into flames!) and after an hour or so the LED became dimmer. Then I took it apart. See the photos. The good news is that most of the volume of the thing is filled with the actual battery. The bad news is that the control chip is very small and apparently easily destroyed. Some other reviewers reported it failing and overheating while plugged into a normal USB charger, and in one case it "fried a laptop".So what is the actual capacity of this battery? I tried again (since I still have 3 good ones left), with a simple resistor as a load. 25 ohms, i.e., a current of about 60 mA (1500 mV / 25 ohms). It discharged from full to empty (control circuit turns it off) in about 15 hours. I.e., the capacity *at 1.5V* is about 900 mAH (60*15). I tried 3 times with 2 batteries and the results were fairly close. Compare that with the claimed capacity of "1200 mAH" (at what voltage?). Close, but not quite. More importantly, that's at 1.5V not 3.7V. The energy capacity is about 1800 mWH (1.5V * 1200 mAH).Charging it via a USB meter I found that indeed it charges in a little over an hour. But the charging current was 0.5A, not the 1A claimed. (The charger I used can supply 2A.) From empty to full it took about 550 mAH at 5V. That is 2750 mWH of energy (550 * 5). The reason that is quite a bit more than the battery's output of 1800 mWH is due to the inefficiencies in all the steps: 5V to 3.7V conversion, battery charging and then discharging chemical reactions, and 3.7V to 1.5V conversion. 1800/2750 = 65% overall efficiency. That's what you would expect if each of those 4 steps is 90% efficient (0.9^4 = 0.65).The cheapest NiMH AA batteries hold more than the 900 mAH output of this battery, and the best up to 3 times more. So this battery is relatively low-capacity. Is it useful? For some purposes yes: the lithium battery has a very low self-discharge rate, and the output is a very stable 1.5V from full to empty. The output current is probably rather limited (given the wimpy control circuit) so I wouldn't use it for high-current devices (such as the shaver some reviewer mentioned). Even a high-powered LED flashlight may be too much for it, let alone a camera flash.