Here's a picture of my Samsung Galaxy S2 battery usage page. Around the point where the battery usage started diving, I had added a calendar remainder, sent an email (to a new contact) and browsed facebook (using their app) and twitter (using the web browser).
I've done all of these things many times before. What could have caused the sudden drain, and how can I stop it happening again when I'm not near a charger? (Updated question after picture.)
I've done some experimentation and made some observations. My workplace is in a 3G dead zone, but has 2G thanks to a repeater box someone has installed nearby.
For the past three months, I have left the phone with 'Sync' and 'Packet Data' switched on all the time. When at work inside the 3G dead zone, I sometimes switch on wifi. Before this incident, I've had no problems at all with battery power, despite leaving Sync on all the time.
After posting the original revision of this question, I charged the phone up while it was switched off, went home and only switched it back on when I got home. I had sync and 3G data all night and the battery wasn't rapidly draining.
This morning, the only change I had made was to carry it with me into my workplace and put the phone on my desk. I didn't switch anything on or off, I only carried it to my desk. It very quickly started heating up and I noticed that battery was rapidly draining as before.
I began to suspect that the dead zone was causing the problem. To test this hypothesis, I charged the phone up and switched off wifi, sync and packet data. During the day, I switched on wifi and sync in various combinations. (Text continues after picture.)
The kink in the graph is around 20 minutes where wifi and sync were both switched off, but packet data was switched on. During those 20 minutes, the phone was heating up and the battery was draining. When I switched packet data off, normal battery use resumed.
Conclusion: Something in my phone has a bug where the battery starts draining badly while in a 3G dead zone and packet data is switched on.
Remember, this only started happening very recently. I've had this phone since January and have left both packet data and sync switched on almost continuously. I've not knowingly had any software updates recenty and the 3G data availablity of my workplace has been consistently very bad for some time.
Does please anyone know of a fix?
(Many thanks to m'colleague Duncan Large for taking the pictures and helping test the hypothesis.)