Help! Both of my brothers' Xbox one controllers lose connection intermittently - tried...

Hello,

I was wondering if anybody would be able to help.

My brothers both have xbox one controllers (genuine branded), and for the last 2 years or so, they've operated without issues. That was until about 2 weeks ago when one of the controllers (lets call it controller A) started disconnecting every minute or
two, the light flashing on the controller and the console prompting us to reconnect the controller. I'm alright at fixing things if I can find out how via the internet, and replaced a joystick module on controller A a few months ago after it kept drifting
- i digress. Basically, it ended up with me so I could try and fix it. I looked at the suggested advice and have tried all these things:

- resynced it to the console

- powercycled the console

- moved the controller closer to the console

- checked for controller updates (its up to date)

- replaced the batteries. (Up to this point we were using a rechargeable battery pack, but i tried with brand new AAs too.)

None of this stuff worked, and controller A still has issues.

Controller B then started showing similar issues yesterday, not quite as frequently as controller A, but enough to make them playing a game of fortnite impossible.

I have considered that maybe I am the cause of this, after fixing controller A's joystick module, but in fairness, it worked perfectly for several weeks after I fixed it and I was very careful, and it seems that controller B has developed the same issues
despite me not going anywhere near it.

My question is, what could be wrong?

I would love to get them two new controllers but with the price being £60 a pop at the moment, it's really not something we can afford, but with lockdown continuing, them playing games together keeps them entertained for hours so is of high importance to
them, understandably. Any replies are greatly appreciated.

:)