You're comparing apples and oranges, sorry couldn't help myself.
Comparing your Mac to your Acer isn't a very good comparison. There are lots of factors that effect battery drain, the main one being hardware. As mentioned power settings will also effect it. One of the big determining factors is how big the battery is (how many cells) and what type of battery it is. You have to be careful where you buy your replacement too. Sometimes that really good deal ends up being a not so good deal. My Aspire 5920 will last a little over 2 hours if I set my power options conservatively. It's not a new battery so I try not to push it much past an hour and a half.