I browse the chan usually every time I'm in class.
I've always found it a bit tedious to scroll through 50 posts, since about one or two posts take up my entire moble screen. Even if I zoom out, it still fills quite a portion of my screen. I personally don't need 50 of them, that seems like quite a lot to fill up a page.
I'd say maybe a margin around 25-10 would be just fine, even for a serial thread. You can leave the 50 option, of course, if that's possible.
I just always found it difficult to get to the bottom of the page when I have to scroll through large posts on a small screen, and I just wanted to skip down to the bottom. A smaller post count would make things more simple.
I've also had issues with the auto updator, and it being a bit difficult to select the 'update now' button, since I first have to choose the +_ -_ thing, which appears next to the reply box on my phone. It keeps thinking I'm selecting the reply box, so it gets a bit annoying, and when I do get into the update options, it seems to have a hard time registering it.
That's just my opinion, though. My battery seems to drain really quickly when I'm using the net on it as well, but that might be from using the net in general. I'm not really a phone expert…