bump - Rechargeable 9V Batteries - 4 Pack Lithium Ion Batteries with 4-1 Charging Cable - Fast and Long Lasting USB-C Charge - Ideal for Smoke Detectors, Fire Alarms, Transistor Radios and TENS Units

So the jury is still out on how long rechargeable 9V lithium batteries will last in smoke detectors, and if one brand is better than the others. Here are the numbers...Energizer Ultimate Lithium 9V Battery which seems to be the standard by which other batteries are measured, and is my preferred, has 1000 mA continuous discharge. Do an internet search for "Energizer L522 Datasheet".I prefer the Bump 9V rechargeable as it feels solid in build, but it still has that strange light weight associated with Lithium ion batteries.The TQTHL 9V Rechargeable battery claims 13500mWh, which is 1500mAh at 9V, but the voltage varies over time, and using mWh feels like a marketing trick. The product feels like it is half baked, as the product description and manual have contradictions and discrepancies, and the housing feels cheap. Shortly after I received mine, it is listed as "Currently unavailable". I believe some companies are using Amazon Vine for QA testing of unfinished or prototype products.Searching Amazon, you will find 9V lithium rechargeables from 600mAh to 1300mAh, so by the numbers, the rechargables should put out as much energy if not more than the Energizer, but the problem may be holding charge over 10 years, which the Energizer Ultimate Lithium batteries claim. I have found that to be true in my experience with the Energizers. Rechargeable batteries usually do not hold their charge over time.Product benefit...So if you need a 9V battery and find a dead one in your device because you didn't properly turn it off or you just got a bad battery, any of the 9V rechargables will help you in a pinch.Back to this battery... the charge time is as expected, and the light was green as described, and the devices I tested it on did not show any low battery warnings when fully charged. In other words, no unpleasant surprises.I am a big fan of the Energizer Ultimate Lithium 9V Battery, but I am not going to pay $12 for a throw away, when I can get 2 rechargables for the price of one of the Energizer 9V. However there is a question of longevity for any 9V lithium rechargeable, and in a smoke detector, you might want to stick with the Energizer. More smoke detectors are coming with built in lithium ion batteries, so I don't really consider this a relevant point, as there are many other devices that are within a hands reach that use 9V batteries. So for the foreseeable future, 9V batteries will be a staple of our electronic lives.PROs:+ Rechargeable+ Lithium+ USB-C+ Light weightCONs:- Will not hold charge as long as disposable

The bump 9 Volt Rechargeable Batteries are a convenient and efficient option for devices like smoke alarms, radios, and electronic toys. The lithium-ion batteries charge quickly and hold a strong charge, making them a reliable choice for high-demand devices. I like the added convenience of the included USB charger cable, which makes recharging straightforward.These batteries are long-lasting, which means fewer replacements and more peace of mind, especially when using them in essential devices like smoke alarms. Overall, this 4-pack is a great option for anyone looking to switch to rechargeable 9V batteries and cut down on waste.

Long lasting and easy to charge. Works just as it should lightweight easy to store. Very long battery life

I don't like the idea of buying and throwing away batteries, so I like to get rechargeable when I can. These are great for remote control toys too! They're very light compared to regular 9v batteries. They use USB-C to charge, very nice!

I ordered a two pack of these and liked them enough to order four more. The only problem I have had was with the newest four i got one that will not work says its charged shows the green light but will not power up my devices. Overall its a good price as long as the quality isnt a 25% loss like my last order. Not many options for the 9v size. 650mah is about the average size I seen for Li-ion 9v the usb-c charging is nice and the provided charging cable is also included.

I have a fair amount of devices that use 9V. I've been needing to replace the battery in my IR thermometer that I use in the kitchen all the time. The batteries in this set fit right in and everything works well. I measured the voltage of the batteries and all of them output in the 9V range. Save money and save the environment by using rechargeable batteries.These 9V batteries have a USB-C port on the side to charge up. The set also includes a 4way splitter USB cable. These batteries are physically the same size as other 9V batteries so you can use them anywhere 9V batteries are needed. I use a lot of AA and AAA rechargeable batteries but not 9V rechargeables. My AA/AAA battery chargers don't have the terminals to charge 9V batteries. Most battery chargers do not have the terminals to charge rechargeable 9V batteries. These USB rechargeable 9V batteries solve that issue by not needing a special charger. Just plug them into USB.These are a great value. I will be purchasing more of these as my 9V devices need new batteries.

Have previously used / reviewed Bump rechargeable D cells and found them to be a good choice. They still work after 3 years.These 9V “square” batteries are a similar aesthetic but have a USB-C port on the side for charging, rather than an integrated USB connector (makes sense for this form factor).I’m typically using these in guitar pedals, guitars with active pickups (e.g. Fishman Fluence) and some toys.Longevity is fine for those applications.Pricing is reasonable when you consider the claimed 1200 times use.It’s also reasonable when looking at non-rechargeable Lithium batteries that cost almost exactly the same. True, they’re double the mAh but for single use that’s crazy.Happy with the specs, price and the performance.Will update if there are any issues but track record with their rechargeable lithium D cells makes me optimistic.

Got these to replace the regular batteries in our smoke detectors at home. They come with the cable needed to charge all 4 at once which is nice. They are USB-C charge which makes it even better as you can use any charger to get them charged up. They charge to full fairly quickly too. The battery life is amazing, we have had these in our smoke detectors for 5 months and they are working well. We test our smoke detectors weekly and they are holding strong. Overall very happy with these and will being more from this brand. Highly recommend!