
My HTC Legend usually used to give a battery backup of more than a day, on Zain network @ Kuwait.
This vacation as I was in Kerala, activated BSNL 3G and then I started facing the weird issue. Battery was draining out like anything, like if i had a Full battery @ 10 PM night, by morning the battery will be totally drained to 10% (Note that the phone is just in IDLE mode whole night).
So my initial thought was that some thing is wrong with the battery and should be replaced with a new one. So searched for a HTC service Center and found one @ Pattom , Trivandrum.
The moment I told the issue to the Techincal guy, He just asked me “Are you on BSNL” , and i said “Yes”, and he concluded “just change to some other network and it will be fine”.
He said lots of people are coming complaining with the same issue(eg HTC wildfire users). And so i did the same and Yes the battery was working fine .
So the verdict, Some thing is wrong with BSNL 3G network or HTC

Few days back I came across this article http://gizmodo.com/5740076/giz-explains-why-your-call-dropped , and it was wriiten that
“On just about any 3G network, carriers transmit voice signals with CDMA, or code division multiple access. (Yep, this includes HSPA 3G, which is often referred to as GSM.) What this means is that multiple phones can transmit over the same radio frequencies, and their signals are differentiated by code. (Disclaimer: this is a brutal simplification.) As one network engineer told me, sharing a cell tower is like sharing a room with a bunch of people that speak different languages. Different people can hold concurrent conversations, but everyone can understand what they need to—their brains block out the rest of the conversations, because to them, it’s all just gibberish anyway.
Just like in this shared room, though, as a tower gets more crowded, the volume starts to rise. The more everyone speaks, the louder one has to talk to be understood. Likewise, the more people that are using a cell tower, the more power each phone needs to be “heard” by the tower. This actually results in a contraction of the cell’s coverage area. “
So it should be the BSNL 3G network which is eating the battery as there are one or two tower which is 3G enabled in a district, HELL who knows.
BTW am back on Zain network and battery life is back as usuall