4-Pack Ryobi USB Lithium 2.0 Ah Rechargeable Batteries

Just since 18650 batteries have been mentioned a couple times already but nobody has mentioned it, it's worth mentioning that 18650 batteries are NOT meant to be consumer-used batteries. They lack the incredibly important protections for being resilient to both physical impacts and electrical problems. In other words, they don't have the armor/protection nor the electrical protection to "just use" them in their raw and native forms by consumers.

If you're building a protective enclosure and building power-protection circuitry to be used with 18650 batteries, that's great. And there are even be some 18650 batteries that do have such things built-in, but the far marjority of cheap ones do not and should be treated as though it's a drop, cheap charger, or power hiccup is likely to case a fueled fire/explosion. That's not to say they'll explode every time you drop them, but there have been a lot of fires recently because people think these are just "bigger and more powerful batteries that anybody can use". Despite cheap Chinese gear taking them, that's a pretty dangerous thing to use unless you're using them responsibly.

Now, should you do it? I can't say. That's up to you. Plenty of people have been just fine. But some have also lost their homes because they didn't realize this. So, it's up to you. I'm just posting this so you can make an informed decision. :-)

(This reply is not meant to single out HonestSoda100 - I'm just referring to that reference to the 18650 batteries. As HonestSoda100 suggests, there is quite a rabbit hole to go down if you do want to use 18650 batteries. This is why you have to pay such a high price for Ryobi's version of them. Or any other repackaged 18650 battery like this deal lists.)

Some sources:
- https://www.cpsc.gov/Newsroom/New...er-Devices
- (gruesome warning) https://www.nbcnews.com/health/he...s-n1032901
- https://www.today.com/news/loose-...or-t208884
- https://www.theatlantic.com/techn...ng/587005/
- https://battlebornbatteries.com/d...batteries/

The use of Ah or mAh is misleading to a degree in terms of comparing capacity. Voltage is just as important. The capacity of a 2500mAh AA battery is 2.5Ah at around 1.3V lets say (which varies by cell chemistry and actually varies with discharge but that's a whole other discussion). That puts the watt hour capacity at roughly (2.5)*(1.3) = 3.25Wh per Ni-mH rechargeable AA. This is 2Ah at 18V, which is (2)*(18), or around 36Wh, which is around 11 2500mAh AAs worth of energy. A 2Ah battery is a lower capacity battery as well.

* Watt hours is a unit that is universally comparable, so you can compare everything from a AA to the battery pack on a Tesla model S accurately if compared in watt hours. Capacity can also vary with discharge current and temperature, but that is further down the rabbit hole.

Then clearly this isn't for you if you have no idea what it is