I bought a brand new Lenovo one on Amazon for $80. I just don't trust 3rd-party batteries, and twice the price was worth the peace of mind. And it comes with a 12 month warranty!

http://www.amazon.com/gp/product/B001QWRTVY

And one thing I've found if the power manager gets angry at your new battery, is to uninstall the program and reinstall it. It didn't like my new legit battery, did that, and it was all smiles from there.