Steam Deck

I find a mix of heat and isopropyl alcohol (at least 70%, though I prefer 99% if I'm working inside an electronic since it evaporates quickly and is less likely to cause a short due to residual liquid when you're done with the repair. Do note that 99% will likely require you to use more alcohol overall and may not be ideal.) works best to remove adhered batteries. I would say using a heating pad is a safer option than a heat gun in most cases (if set to about 72-76 degrees Fahrenheit, for about 10-15 minutes). Usually you lay the device face down (never put it on where the battery is directly touching the heating pad, too much heat can cause the battery to catch fire or explode) to loosen up the adhesive. All that being said I'm not sure how well it would work with the steam deck though since the control sticks make it hard to lay down flat, plus I don't know how the heat will affect the screen (most devices like phones are usually fine as long as it's not too hot and not too long).

If the battery is expanding you should probably not use heat and just isopropyl alcohol as inflating batteries are more at risk to catch fire or explode. If you can't, or don't want to use heat then you can just use the alcohol to slowly pick away at it, but it's going to require more patience and take longer. Also you're more likely to tear up the plastic card you're using to get the battery out.