Why is the rechargeable battery for my electronic device bloated?

Question

I have this electronic dictonary which uses lithium ion battery to work. However i found out that after leaving my E-dictonary untouched for months, the battery actually gets bloated. The same thing happens to the battery for my former cellphone which i have left untouched for a few years.

Can anyone tell me the cause of these bloated batteries and is it still safe to use these bloated batteries for my electronic devices?

Answer 1

Poor quality battery. Have it replaced.