Just read this over at CyanogenMod:
(CELL STANDBY FIX)
"Seems as if there is some sort of bug with with Cell standby that causes the phone to lose signal which in turns just kills the battery. To verify that your set has the problem, check the Cell standby info in the Battery Use info. If the Time without a signal is higher than 0% (50% seems to be the norm) than you have a problem One solution, at the moment, is to follow these steps
1. Plug in phone charger
2. Put phone in Airplane mode
3. Put phone to sleep for a minute
4. Turn off airplane mode
5. Unplug phone"
Not sure Of the validity... but some people are saying it fixed the issue... assuming it hasn't already been posted here.