My wife's laptop needs a new battery. I think she leaves it plugged in too long and never discharges it enough. Still works but only holds a charge for maybe 20 minutes tops.
It's a ASUS K52F

Any suggestions as to where to get a replacement?

Amazon and Ebay is a great sources for laptop batteries.

Yep the best two places

Reckon I have the same problem with my HP  pavilion. Ebay it is