PALO 2 Pack 9V Rechargeable Battery Lithium Li-ion USB 650mAh with 2 in 1 USB Cable for Keyboard Microphone Smoke Alarm

I'm an electrical engineer who has been testing a mess of rechargeable 9v lithium batteries for a recent project. Ran this one under a 21 ohm load. It took an hour and 34 minutes to discharge via 21 ohms, so a pretty intense .6C discharge rate. The photo is a plot of the voltage drop over time. I calculated 3626 mWh capacity by multiplying and summing the second by second voltage and current readings. Bottom line is this is one of the highest capacity, internal USB rechargeable 9 volt batteries out there.

I use these for my in ear monitors at live shows and rehearsal. I recharge them after every show so I do not know how long they actually last. I wish they were back in stock! I bought another brand of rechargeable 9v battery that did not fit in my monitor receiver pack.

There isn't just one number for a battery mAh rating, because it depends on your voltage endpoint. All so-called "9V" batteries on the market droop a long way before giving up completely. Of course the mfr. will quote the most favorable number, but some devices do not work at 6 V. If you need at least 7 V for operation, then I measured these to provide 431 mAh before reaching the 7 V level. This was at a very light load of 4.22 mA so discharge took just over 4 days. In my case I was using two in series, so my chart goes from 16.6 V to 14 V but just divide the numbers by two to get volts per battery.I find this performance pretty good, and the built-in microUSB charger is convenient. I have tried other batteries that do worse.

these are great now I dont have to worry about needing battery for my volt meter again .great idea

Measure 8.6 V after 2 hours use… keepers

Unexpected bonus: Cases to put AAA batteries in so can be used as AA batteries. Clever!

These 9v Batteries perform well , and supplied just slightly under 9v . The difference was only a few 10th's of a volt , and this might have been my volt meter not showing correct voltage . They charge from my PC USB with no issues . The Batteries have red and green charge indicator Led's inside . Good quality charge cable as well .

Garbage. One didn’t work. The other doesn’t keep power. Not even worth returning.

Used in a guitar with active pickups. In general we're not supposed to use rechargeables due to poor performance, but these provide a high enough voltage for a long enough time to work great! This is after a couple months of testing and wear.

They max out at 8.7 volts when fully charged but connected in parallel, they'll easily last as long as I need them to. So much cheaper than buying Alkaline batteries and charging both batteries at once is simple with the provided USB cable.

Still not bad for the money