I tested the NiteCore NL1835HP 18650 3500mAh battery on the NITECORE MH25GTS flashlight at the HIGH 950 lumens setting. After 1 hour and 45 minutes, the blue indicator light started flashing slowly to indicate that the battery had lost over half of its charge. At 2 hours and 15 minutes, the battery had almost completely discharged and the battery level indicator light started flashing rapidly to indicate that the battery was almost empty. However, the flashlight maintained the same level of brightness as when I first turned it on with a fully charged battery. At 2 hours and 24 minutes, the flashlight suddenly dropped to 1 Lumen brightness, indicating that the battery had very little charge left. At this point, I did not try to increase the brightness as it was almost empty and in need of charging. In conclusion, the battery is more than excellent because it provided consistent brightness for over 2 hours and 15 minutes, which is longer than what the manufacturer claims. It is a great battery for its performance and durability, and it is worth the price. Consider using this battery in a device that consumes less power than what the battery provides, as this will significantly increase its lifespan. It is an expensive battery, but if you test it as I mentioned, you will see amazing results that you won't believe. Even if it works with devices that consume more power, it will still perform satisfactorily in terms of duration when it is close to dying. If I ever use it heavily in the future like I did today, I will add my observations. I charged the battery using the Nitecore UMS4 charger with the QC3 adapter from Blitzwold, which has two outputs: SPOWER and QC3.0. It took 3468mAh from 3.14 volts to 4.20 volts, completing the charging process in two hours and eight minutes. Keep in mind that this was a fast charge with only one battery in the charger, not two or more simultaneously, as the current would be divided. Although I don't know all the features of the charger, I simply described how I charged it. Update on the battery as of February 23, 2023: It has been 2 years, 10 months, and 14 days since the first use of the battery, with the last charge being in 2020. The battery was inside the flashlight without being fully screwed in, so it accidentally turned on. The battery still has a charge of 3.7 volts and works normally. I want to emphasize that the battery did not leak, rust, or swell despite being partially charged for almost 3 years. I will charge it again to see how it performs after such a long period of inactivity, and if I encounter any issues, I will write about them here.