Battery draining can be a side effect of a lot of CPU usage - is this the case for you (check with Activity Monitor)? If so, and vmware-vmx is the one taking up the CPU, the next step is to figure out why this is happening. See Frequently Asked Questions about VMware Fusion.
I am running xp on fusion on my Macbook Pro (Intel Core 2 Duo 2.2ghz, 2gb of ram), guess OS 512mb of RAM, and whenever I am using fusion my battery life is substantially cut .... on a max charge I am lucky if I can get an hour and 45 minutes compared to about roughly 4 hours without using fusion. I know that using fusion would drain battery a little bit, but is this normal? I have also noticed ever since I upgraded to Fusion 2.0, there has been more lags and it seems to be using a lot of memory (activity monitor reports on average around 20mb free memory) and performance has slowed down. Is it normal to see that much of a battery drainage?
It all depends on what's running and what you're doing and how old the battery is. When I first got my MBP I could leave the office in the morning with a fully charged battery and and be out and about doing various things on the notebook through the day and then charge it back up at the end of the day and as time went by doing the same basic things and the same appropriate amount of work load I had to start carrying around my charger to make it through the day. Now on the other hand if I started watching a DVD or watching videos online my battery would drain before my eyes. Well not quite that bad but a distinct noticeable difference and enough so I couldn't watch a feature length move while on battery. Running a Virtual Machine even if just sitting there is consuming CPU Cycles and thats going to add to the drain caused by the other apps that are running.
Now start using the Virtual Machine and it will chew up considerable more CPU Cycles then the same task on the Mac would, so there is a price to pay when running Virtual Machines on battery and when I need to be running Virtual Machines a lot I typically have the MBP running on AC vs Battery.
my battery is probably almost a year old now. would getting a new one help?
If you use and depend on a battery a lot then other then financially it doesn't hurt to have an extra battery and I'm positive you will see an appreciable difference between using a fully charged new battery and a fully charged 1 year old battery.
Having only 20 MB free mem it's possible that your mac is constantly swapping, resulting in lots of disk activity and this will drain your battery too.....
How much is free without fusion running? And depending on the app in your vm, it's quite possible that your vm is also constantly swapping to the windows swapfile, making things worse...