I have a pair of headphones that I absolutely love(Marshall monitor II ANC). They’re running out of charge within an hour nowadays and the headphones are quite expensive to replace as a whole. I figured I could replace the battery but the company doesn’t sell replacements and doesn’t do repairs. I opened it up and found that the battery is swollen. I’m not very experienced with electronics although I’ve done little things like changing the joystick on a Nintendo switch… but a battery is scary. So I have a few questions.

1. Can I use any battery with the same size, rated voltage and wH? Are there any other considerations to be made? I’m asking because the only battery I can find which even says it’s compatible with my device in the description, is on Alibaba and will take 60 days to ship while there are others on Amazon which will ship faster but do not mention the name of the device.

2. I will be soldering for the first time. Is a badly done solder going to be a health risk considering this thing will be next to my face all the time. Is a badly done solder a risk to completely brick the device or affect sound quality somehow?

3. I found that the charging voltage for the battery is 4.2V. I have been charging it with a Nintendo switch charger which has output rating of 5V and 15V. Is this why the battery is swollen?