Maxwel Manufacturing USB 9V Rechargeable Battery- 9 Volt High Capacity 650mAh Square Lithium Batteries with Type C Port Cable for Smoke Alarm Detector,Wireless Microphones & More (2-Pack)

Works good. I try to use rechargeable batteries as much as I can, to be environmentally conscious. It has a 2 cable charger so both can be charged at the same time. Cannot find rechargeable 9-volt batteries in local stores.

I have several little audio items that run on a standard 9 volt batteries. I was attracted to these rechargeable batteries so I could just charge them with a USB charger and not have to keep buying 9 volt alkaline batteries all of the time. I also liked the little charging port on the batteries, but noticed there were no charge/discharge lights to indicate status. Being an electrical engineer, I measured the voltage on each battery and was happy to see something 9.03 or 9.04 volts, with no load. I assumed they were fully charged already and tried them out in my devices. Nothing. I measured voltage again with my DVM and they both read zero volts. That's odd, first read full voltage, then zero. So I charged them overnight with the a small USB charging device which monitors both output voltage to the batteries and current. Voltage was OK on the charger but the current was zero, which meant the new batteries were not taking a charge. Only when I connected the new batteries to a larger battery pack designed to be a portable charging device for traveling, did both the new batteries take a charge and work when placed in the devices. Bottom line... The batteries are shipped with no charge, but may measure a full scale voltage on a DVM. Huh? If they had battery status lights, like stated in the Amazon ad, I probably could have avoided all of the BS I did at first. I gave this review 4 stars because of the confusion I had at first. I assume these batteries will last much longer that a typical alkaline battery, but that remains to b seen as time goes on.

Is short time but work ok in the sensors

These batteries never worked and would never charge up. Complete waste of $

I thought that one of the two batteries was defective. After further investigation, I found the charge cable was defective on one side. I had plenty of usb c cables so I canceled the return request. I gave it only 3 ⭐️ due to defective charger.

Having a USB C charge port on the side ups the game for these rechargeable batteries. In many applications, you can leave the battery plugged in and just charge it up. That essentially makes your device a USB rechargeable one. Probably a good idea to also make a front side charger port too since many batteries are flat mounted. These tested at 9.22 volts and held a charge for a pretty long time. Easy to recharge using the supplied or any USB C cord. It has the super sensitive short circuit safety feature so if you touch the terminals with a common metal for even an instant, it goes dead and won’t reset unless you plug in the charge cord for a moment. That should be changed to reset after a very brief short circuit ends. I guess they are being pretty cautious and safety first is not so bad. These are a buy.

It took some time to find the Green LED, but it is there and very, very, small. The only thing I don't like is they cannot be recharged with a standard 9V charger, but other than that it does the job.

The first set I received 1 battery was showing fully charged however it only lasted about 4 hours in a smoke detector but when I plugged it in to recharge the blue light came on right away. So I was able to exchange them for another set which so far are working great