Used Respironics SimplyGo Battery. 90 Day warranty.

Lightweight and compact, these new Lithium-Ion batteries weigh only 1.5 pounds! They are easily accessible and can be quickly changed by oxygen users on the go.
Each battery will last approximately 3.5-hours on a pulse dose setting of 2 and 2.3 hours on a continuous flow setting of 1. Batteries will recharge in the concentrator whenever it is connected to AC or DC power.