Well first off, CM is known to be a battery killer, but aside from that, your best bet is to see that no background apps are draining battery on top of CM. A good app to install is Juice Defender, it really does make a difference.
Nasty budget phones, begone! Hello sexy brand new Galaxy S2!
CM7 has improved a lot lately.
Try to update your version with the latest, it doesn't have that much of a drain.
Also remember that all data connections also drain the phone for a decent amount.
If you're still having problems after that, you should consider wiping your data (factory reset and clear dalvic cache).
Start from there and add programs if you need them (monitor the difference in battery usage so you know what could be causing problems).
I use a Samsung Galaxy S and have been facing same battery draining issues over time.
I though that the new ICS update will enhance my battery and phone, but i was much more distracted after knowing that i wont be able to update my device.
now i have no other option to change this device.
Since Nokia is always been into the lime light for its battery output and also i need a smartphone, so i tried the Nokia Lumia.
I am very impressed with this device.
The Lumia is much backed by battery and i now have a big customized screen.