Hello, I’m the developer of WaniKani for Android (https://play.google.com/store/apps/details?id=tr.xip.wanikani). Assuming you are talking about my app:
Firstly, I had never noticed much of a battery drain caused by the app. Well, I haven’t been actively using it for about 9-10 months now, as I haven’t been able to keep up with my WaniKani studies. It might be that a recent update is causing it. I’m finally getting back and did a batch of reviews yesterday. I’ll be monitoring the app for the coming few days or weeks.
Secondly, you said you were getting “failures” and error messages. What is happening exactly? Do you mean crashes? I don’t think the app crashes nearly enough times for it to become hard to use. Is there something exceptional going on, on your device, perhaps? Can you provide some more details please? Also, can you write about this on the app thread (/t/Client-App-WaniKani-for-Android/6035/1)?