I have the same experience here. I used to run some old phones 24/7 (plugged). One day I noticed that a battery is swollen and decided to retire all of my phones. It is not worth to risk a fire for low performing phones.

My opinion (I am not a battery expert):
If you battery is swollen it is already damaged. So using that battery is risky.
If you plug it in (to a computer) it will be charged. Charging a damaged battery does not sound like a good idea. So I would not use that phone anymore! In case you really need the data on the phone you should bring it to a repair store and get the battery replaced.
If you decide to take the risk and plug it in, safety actions should be considered.
Maybe someting like: Do it outdoors. Place your phone on "fireproof" ground. Put it in some fire blanket in case it starts to burn/explode? Keep distance...
Once again, I recomment to not use that phone anymore. Plugging it in sounds dangerous to me.

And one think I would like to add: Even if your phone is not plugged in atm, the battery might still be loaded with some energy. Stored batteries can explode as well if they are damaged. Unplugging your phone does not mean it is 100% safe now.

I checked. So sorry to tell you that you probably won't be able to use it again. look at the image I pulled off a website. The battery is LOCKED to the phone itself. Without a special tool, you won't be able to disassemble it. Can't you take it to an ASUS service dealer? 3yr is not a long time, they probably still provide service. Just tell them you need some of the data.

Jackie, yeah I know, I cannot change it by myself and wouldn't dare anyway. haha. There are many phone stores all over Taiwan that can do it for me, they provide all sorts of services like this, the problem is it may be too old for them to be able to get a battery for me. I will go to one store today to check what I can do. But I don't know how to transport this thing safely at this point. So freaky. Getting service for phones from Asus directly anymore is quite difficult, most everything is transferred to China, which doesn't help me locally.

I did notice my Lenovo does not get so hot, so you are right about the newer chips. But it is not so much the chip getting hot, but the battery getting hot from overcharging. I have an Xperia X Performance that also gets bloody hot now just from normal use, and it too has a slight bulge. But I trust Sony much more than I do Asus. But still.. Another ticking time bomb.

And my Sony XZ3 also does not get so hot, but that is my main phone, so I aborted everything and removed the app. I cannot risk my main device having problems.

Android devices are just toooooooooooooooooo slow. haha. My i9-9900 cpu in my main machine can do 16 WUs on covid 19 in 2.5 hours or so. But it is only one device.

And indeed actually I scaled back on how many WUs I was doing on the phones from 4 to like 2. But you are right, just doing one is probably much safer. But still risky. And if I replace any of the batteries they will not be factory battery probably, so which means it also carries risk. You know, so many aftermarket stuff like this in Asia, so some are safe and some are not. Hard to tell.

I see you are running many Android devices... Never get hot? You don't worry?

@lava, I was told that even the old phones were supposed to do that. lol. but........... seems like that is not the case at all. Scary!

I can say that my Lenovo pad does not feel hot at all. And it will run when not being charged up til the low amount I set. so I set it to 40%, and it will stop, but I usually plug it back in sometime around 50-80% of full so it will keep crunching. I have 3 cores running on it, I have 29 results from that device in about 4-5 days running. Much more than any of my other smart phone devices that I have now turned off completely. I plugged in an old HP notebook, it seems to be able to do about 9 WUs a day. I pulled the battery off of that so it won't even think about charging and only use AC. Just if power is lost.. well...