Recommendations for macbook battery

I have an early 2011 13'' macbook pro unibody and a Newer tech nupower batter I bought in November 2014. The design capacity is 58.8% and the trackpad has become a bit stiff. I suspect the battery has swollen.
What brand of battery would you recommend? Are eBay and amazon reliable places to buy mac batteries (I bought this battery from owc)?

If you suspect the battery has swollen, then you should immediately remove it before it does any further damage to the trackpad or even the keyboard. As for purchasing another battery for a machine that old.. Amazon, eBay, are OK. The batteries you see on eBay for the most part are cheaper knock offs but as long as they work and give you 3 or 4 hours of battery time, should be OK to buy.