Laptop battery question

[rincal]

i have a dell inspiron 1750 that says plugged in but not charging, it works fine when plugged into power source with or without battery inserted.

my question is: how can i tell if it's the battery that is defective or the laptop? I don't really want to pay for a new battery to find that the laptop has the problem.
thanks in advance.

 

[Emerald]

usually the life expectancy of a battery is about 2 years

 

[John2013]

You'd better to change your battery