I am currently developing a vanilla (no mobile frameworks like sencha) mobile web app I can attest that on IOS you can pretty much get native performance if you do some trade off and optimize your app rendering.

On android that's another game and you can forget about all those cozy animations and only devices with android 4.0+ will perform well, or at all (in my case anyway).

Also I'm really not sure why people currently associate html5 apps with bad battery life, personally I did not see any noticeable differences in usage from a native one, hell native use a lot more the gpu so it should be worse.