Is less than 2 hours of battery life normal for Galaxy S2 with
To be honest, it sounds like a hardware fault in the phone, especially since you say it's been happening since you bought the phone. If the phone were still new, I'd say you should take it back to the shop, but by flashing a new ROM you've voided the warranty.

To answer your question: no, it's not normal for that phone. I've known a few Galaxy S2 owners, and you should get as much life out of it as any other smartphone: a couple of days between charges if you don't use it heavily.