Screen Goes Black in the middle of doing things

About six months ago I replaced the battery in my Samsung Galaxy Note 10.1. I bought a brand new samsung battery. I am happy to say it was working great until about 2 weeks ago. Doesn't matter what your doing using an app or surfing the net suddenly the screen goes black. Initially I thought it turned off but I am not sure now. You can't turn it on or anything. If I put it back on the charger and wait for the battery charging to come on the screen and unplug the charger you can turn it back on. The battery charge level reads 80 or 90% so it's not the battery being low. Help!