The ring of endurance is a potential reward from the Grand Hallowed Coffin on the final floor of the Hallowed Sepulchre and requires level 70 in the Agility skill to equip. The ring can be charged with stamina potions, with each dose granting one charge. Storing a maximum of 1,000 charges, it costs 1,274,750 to fully charge. The ring counts as a Saradomin item within the Hallowed Sepulchre and the God Wars Dungeon.
The ring provides two effects when charged. First, if the player consumes a dose of stamina potion with the ring equipped, one charge is consumed, 40% of the player's run energy is restored, and the duration of the stamina potion effect is doubled. This effect is immediately halved if the ring is unequipped. In addition, if the ring has 500 charges or more, it will passively reduce the run energy drain rate by 15% without using any charges. All of the stamina charges are lost upon uncharging the ring.
For an exhaustive list of all known sources for this item, see here
- The examine text on the ring alludes to whether the ring would help the user last longer during sexual intercourse.