Now that I am finally back in the civilization, I took the phone to service. Let's see what they have to say about it.

On another note: The phone was in a pocket of my water-resistant trousers and I was sitting in the pond for only a couple of seconds. The phone had no moisture outside and when I removed the covers and the battery, everything seemed dry. Although it still of course could have gotten some water inside from some other point of entry.

I tweaked around for a day and got the GPRS working intermittently. It would reboot the phone 9 times out of 10, no matter whether I was using 2G, 3G or dual mode. WLAN would not work at all. The temperature seemed normal, maybe last time I checked it, I had just used the phone heavily/charged it/something, cannot remember.

Anyway, the original battery dying might indicate either water damage or some other damage (I did fall, I might have crushed the phone with my weight or the phone might have hit the rock).

We'll hear the judgement from the service at some point in (I hope) near future.