I havent experienced the WFire S but I had htc wildfire months ago. I dont think that you should really worry about battery. You can download various softwares from android market which helps alot. Power saver software took my battery life from one day to 2+. Sometimes even 3 days.
Though It was my primary phone, but again that depends upon your usage. FYI I didnt use battery draining apps that affects like cam, mp3 or wifi.