Been using old phone for white noise for the little one for over 2 years now.
Today I realise the battery is swollen, so time to throw it away and look for a new one. Looking at ebay, those so called geunine Samsung battery are like $10, which pretty much mean they are fake anyway.
Since a mobile phone can't just plug it to wall plug without battery, Is there any alternative that is an android with speaker, that only use AC power so i don't need to worry about another swollen explosive?
Are you sure? Older Nokias used to be able to be used without battery when plugged in. Also a $10 battery for older devices isn't necessarily fake.
There's also several white noise dedicated machines on eBay around $15-30 so have a look if that suits you better.