i dont know what you have removed from the OS that makes it slim, but it is very buggy,
buggs donot mean just crashes, (because there are none, its very stable) but this one is a battery guzzler. i went from 100% charge before sleeping to 50% and reducing fast when i woke up. its been 1 hour since and the battery is already at 36%.
i checked the usage and it shows Gallery as being the culprit. 22% usage. android system 18%. WiFi 15%.there needs to be some look into the rom because i have tried Slim ICS many times but the bettery drain always puts me off.