I got two packs of four of these to try out. Before putting them in a device, I checked them with a multimeter to see if they were really lithium. They consistently gave 1.5V as they should (they have a small buck converter that drops the voltage from 3.7 steadily to 1.5). The only strange thing was that in each package there was one completely empty battery, which made me a bit concerned about whether they were "dead." Nevertheless, when I charged them, they worked fine.

The other 6 I fully discharged and recharged, and put them in the well-known "battery eater" Game Gear with the original screen (old-timers know...). With fairly high brightness and the speaker at max, they lasted 6 hours and 35 minutes! Also, they didn’t heat up much, which is a plus.

However, I should note that when they run out, they do so suddenly—they don’t have a gradual voltage drop. So they’re not ideal for devices where you need to see an accurate battery indicator. As for their longevity, time will tell. For now though, in terms of performance, I’m very satisfied.