I’d take the 50% and not buy from AliExpress again.
I’ve only ever bought direct from Anker or Soundcore or their direct on Amazon and had zero issues with the few times I needed to return. Just last week I got replacement Q30 and posted back a unit and they credited me the postage costs.
Any issues you have arisen via how you bought them based on my experience.
It is a puzzle why it’s a dead unit. They are tested when leave manufacturing so I’m thinking either damaged (package should show that) or it’s been in bad storage place for a long time (kept too cold or top hot and the lithium was ruined). The Q20 is the previous product so could have been stored a long time badly.
All the Anker products I bought which have batteries inside have been recently released so it’s impossible for them to be stored a long time, I then store them at home at cool room temperature and their batteries last 4+ years.