Hi there,
I have WiFi and 3G always on, 3 mail accounts on 15 minute sync, write 20 SMS and take 5-10 calls for 2 - 4 minutes, browse for 10 minutes, take 5 photos on average day and the battery lasts for 40 - 48 hours.
When I installed Whatsapp, my battery drained like you described, so I am...