If you just re-added everything, the kindle will re-index everything and eat at your battery for a while. That might have been what cause it to drain so fast 'afterwards', but I'm guessing you only did that in the beginning because the battery was dying anyway.
Nothing wrong with cheap. Just make sure you get it from a source you can trust and make sure its a genuine KDX battery. You want to avoid third party batteries if you can. There usually isn't anything wrong with third party, but from my experience they might have less capacity or give false readings on remaining charge on the battery.