Just saw that my mid 2010 MBP battery is saying "Service Battery". 1. Does this mean my battery is starting to die and I need a new one?
2. If so how long will this battery last me? 3. Is it something I should get fixed immediately? 4. How much will it cost me? 5. Is it worth fixing or is this a good excuse to get a new MBP?
I numbered your questions to make it easier to answer.
1. You should keep a close watch on your battery. LiPo batteries tend to swell up when they near their life's end, this could cause trouble with your trackpad not clicking, for instance. (apart from a battery life much shorter than when new, of course).
2. Impossible to say, unless you have a crystal ball lying around you could lend me. It could be years or it could be days. I've had my older 2008 say service battery for the last 2 years with no ill effects.
3. Not really, no, just keep a close watch on it (see #1).
4. $129 at the apple store, not that a quick search of Apple's well made website would've told you that.
5. That depends entirely on your very own definition of "worth it" and whether or not you have enough disposable income or would actually benefit from the newer machines. The mid 2010's are quite capable. Since you did not say what you actually use the computer for, your question is impossible to answer.