Controller Disconnecting

So I have two Xbox One S wireless controllers (one of them is broken and I posted about that earlier), and when both worked, I would connect one to my phone. It connected fine, but if I left my controller idle for about 20 seconds, it would unpair from
my phone, therefore I would have to reconnect it. I still have one wireless controller left, and I can connect it to my phone. It disconnects after about 20 seconds. Occasionally, though, it connects automatically and won't unpair. It will just stay connected.
If someone could help me I would greatly appreciate it!

:)