Sometimes a generic battery will not allow for battery health or capacity. Depending on where you got it, it might just be a bad battery. Personally, I would get rid of it and buy one from iFixit. I have bought several, and they are top notch quality. They may be more expensive than ones from eBay, but they will last so much longer. iFixit also has a warranty on them so you don’t have to worry about it.

Check the distributer. I was traveling down the highway, and it was running rough, so I slowed down and ended up going 20, before having to just finally pull over. The bearing had gone out in the distributer. I bought a new one for about 200, installed it, and it runs great now, 30,000 miles later. I'm at 230,000 now. 2001 Nissan Xterra XE