Smartphone battery replacement recommendation

I've got a Samsung Galaxy S8, which I've had for 3 years. I love it, and have no wish to "upgrade", not least because I believe it's the last Galaxy model to have a headphone socket as standard. Trouble is the battery has VERY short-life, only lasting a few hours on moderate use, and liable to plunge from 20% left to dead literally in seconds.

Well, today I got new phone battery, and wow! I'd forgotten what it was like to not have the % dwindle in front of my eyes, like sand through a colander.

For locals, I can highly recommend Walk & Talk, that tiny little shop right by Harringay Green Lanes station. He not only fitted a new battery, he also did something to the troublesome USB-C port (which has a serious design flaw), so that it now works properly with all my charging cables - and all in about 15 minutes.

I had initially asked at Fastech (who are very good with computers, but maybe not so hot on phones), and they said the battery replacement would take a whole day (and they couldn't get a battery from their supplier anyway), and that there was nothing that could be done about the USB-C port.