Mine is working very well until now. I bought it 2 months ago - or something like that -, and the battery stills going through the day without making me angry.
Using 3g/4g at almost full signal, a lot of WhatsApp and music during the day, and after 14 hours of use I still have around 50% of the battery left. I'm really really happy with the battery life of my 830
Now I'm facing a very hot summer here, lets see if the high temperatures will affect the battery life in any way. I remember that my 820 was literally burning the battery during the last summer. 100% to 0% in less than 8 hours with the same use as my current cellphone.