After only a few weeks of use my device is already running slowly. Apps are slow to open, and some run poorly or are...

According to Blake Stimac, a staff writer at greenbot.com, (You can find his article here) the battery life should last around 9 hours of HD video viewing. By turning on power saver mode, you can extend your battery life at the cost of performance. If your battery life is significantly lower, you might want to try closing some applications, or if worst comes to worst; replace your battery. Here's the troubleshooting page if it helps.