Glacially slow charging speed HTC M8

OK, so I have a six year old HTC M8 that is in pristine condition having been in a HD case since day one.

It had a new battery a couple of years ago.

Recently it’s been charging really slowly and cutting out when using the camera. It was showing an error stating ‘slow charging - use a HTC charger /cable’ (or something like that).

So I took it to a local tech guy whose work I trust. I asked him to replace the battery and the charging port/board/flex.

It’s not worked and it’s taking 24hrs to charge to 100%,. I can’t work out whether it charges faster tuned on or off. When charged, it holds the charge really well.

I know the phone is six years old but it’s immaculate and works great when it’s got charge. I’m trying to get to ten years. Hahaha

Anybody got any pointers please?