Deleepow 9V Lithium ion USB Rechargeable Battery, High Capacity 650mAh Rechargeable 9V Battery, 1.5 H Fast Charge, 800 Cycle with Micro USB Cable,4-Pack

Work on my fire alarm without any problem.

good value, don't buy throw away batteries again

1 of the 4 batteries "puffed up" similar to how some cell phone batteries will when defective. It may have been that the power source was inadequate (I had it on a USB hub in a pinch as opposed to a charging brick). Overall the batteries are good, but I was surprised when I saw the bloated battery on my desk. As for the charge, they are almost on par with standard 9V batteries you would buy in a retail store. They don't last as long as industrial batteries, but work well. If you are looking to use these in a tens unit they won't last too long as far as charge life or overall. I can use these in other things, but the tens seems to have shortened their overall life by quite a bit. Regardless, it was a pretty short ROI given the price of disposable 9V batteries.

Unfortunately we had to send these back because even on a full charge they would not work in a smoke detector. :-(

They work well and charge great over several hours, but two of the four have a defect and on the same charger and cable stop at 7.7v, hopefully seller can correct. At 8.4v they appear to be equivalent to 70% full alkaline, the defective ones are basically less than a quarter, or dead.

I received 2 x 4 packs of these Delipow rechargeable 9v batteries on 6/5/20 and, after fully charging, replaced all of the batteries in my smoke detectors 1-2 weeks later. On each of the past 4 days a smoke detector has begun to beep indicating low battery. I used to replace the alkaline 9v batteries annually as regular maintenance and it's not going to work having to drag a ladder into the house every 3-4 months to remove, charge and replace these batteries. I have 7 smoke detectors so that meant buying 2 x 4 packs at a cost of a little over $60.00. Now I'm to be out more $$$ as I need to buy Energizer or Duracell batteries.

2/4 of these that i ordered delivered a voltage that was too low after being fully charged; thus, the smoke alarm kept saying that my batteries were low and had to be replaced. i purchased the significantly more expensive Blackube USB rechargeable batteries. they worked and have an advertised 100 mAh larger capacity (750 vs. 650), though i didn't independently confirm the capacities myself.

The product showed full charge (green led) after charging but actually has showed only 1 /4 of the microphone levels after installed into the microphone .The Product is very suck. I need the replacement.