Can having a MBP constantly charging damage the battery? I constantly have my MBP connected to its charger. I was curious though, can this affect the battery? If the battery is always at 100% and power is constantly being fed into it, does this damage the battery? Because right now my trackpad is bulging same with the lower body of the MBP and it's because of the battery expanding. So I was curious if the constant charge may have deformed the battery.

Thank you
Constant charging should not damage the battery in an extreme manner. Yes, you would get more life from it if you would let it always cycle between 40 and 80%, but the Mac is already cycling power in the high 90s even though it is not showing it to you. I have not been cautious at all with by 2009 Macbook Pro and I can still get around 2 hours of autonomy from it.

However, a bulging battery is a very different scenario. You should get that replaced as soon as possible. Several people (on forums) have reported that they got their batteries replaced for free, even in out of warranty computers. I would strongly suggest bringing your computer to an Apple store if you can.