Can rooting be the cause of battery drainage? Its been three weeks I have rooted my phone. I have installed a lot of apps using link2sd on external sd card. I have noticed that since the rooting, the battery goes down very fast. 80% of charge goes down to below 40% overnight when on stand-by (without any data/wifi connection). Can the root be cause for that? It hasn't been even a year I bought that phone.

Note: I am using android 2.3.6 and juicedefender for improving battery usage.
Short answer: No

Long answer: It's all the apps and services running in the background, some great apps I use for monitoring what's going on with the phone: 


System Panel [theres also a lite version, SystemPanelLite Task Manager]
CPU Spy
BetterBatteryStats


With those you will be able to narrow down what is causing all the battery drain

Also it may be wakelocks on your kernel