Steam Deck Problem - Won't run off battery

Having this problem with my steam deck where it won't run off the battery but it will charge it and it can see it, but it will only work plugged in and shuts off as soon as it is unplugged. This is my 2nd Deck as I RMA'd the first one for the exact same problem which appeared after 3-4 weeks. I am not using any dock except for the official dock and never used it on this 2nd one (I have only had it for 3 days)