Now that we have seen what the Switch is and what it will do, there are evne more questions to answer. Those questions will probably take months to answer, so the rumors and speculation come up once again.
I want to point out that the tweet above comes from someone that was spot-on with Switch rumors. From design to functionality, she got everything right. She also is the main source behind the Beyond Good & Evil 2 Switch exclusivity rumor. I just wanted to make all that clear so you could form the best opinion possible on her battery life comments.
That said, just what exactly does 'mediocre' entail? I honestly don't know, but I can tell you that Laura retweeted someone that said the 3DS battery life was mediocre.