A popular device now old enough that the original batteries are starting to fail from age and use. It happens all the time, nothing about the Steam Deck is special for this, it happens with everything.

Yeah, this feels like extreme price gouging. I generally like what iFixit does, their toolkits are great and I've bought Steam Deck parts in the past (a replacement fan when mine got noisy). However, if they're going to participate in price gouging I'm done with them. There's no reason a Steam Deck sized battery should ever be even close to $180, and given how numerous third party options are, there's zero reason to pay that price for an "official" one. It's a battery, it's as generic of a component as it gets. Sure, it has a charge controller, but so do the third party ones. It's a custom shape, but that's probably just two standard sized cells taped together. If the shape were a real problem the third party ones wouldn't be any cheaper.

AliExpress is a pile of garbage but you can find decent things there if you know where to look. I've gotten quite some decent items from there.

Anyone and any shop can sell there ranging from good ones to scammers.

It's probably made in the same factory, but there is more QA in the chain (normally/I hope) and then the batteries have multiple middlemen taking a cut with IFixit adding their profit margin on top of every middlemen costs.

Wasn't a thing originally, they added it later. But it's habit, I never leave lithium battery devices plugged in. I have a laptop from 2011 that still holds over 90 percent storage.

Yeah, I love that this sort of thing is an option now. I do 80% on my ebike and 90% on my phone. Hopefully that will prolong the life of two of most frequently used gadgets.

The myriad of reasonably priced unofficial batteries on eBay and AliExpress.

2 to 4 18650 cells would work