New MacBook Pro Batteries Much More Expensive to Replace
The cost to replace a battery on a previous generation 13-inch or 15-inch MacBook Pro in the U.S. is $129, which itself isn't cheap. On the mid-2012 models sporting Retina Displays, the price jumps nearly 54 percent to $199, which is even $20 higher than the battery replacement cost for the previous generation 17-inch model.
Not only are the new MacBook Pro models tough to crack open, but the updated batteries are more expensive to replace ($199 versus $129). Image Source: iFixIt
That's direct from Apple, mind you, and doesn't include taxes. You're free to purchase an aftermarket battery on your own, but keep in mind that the built-in batteries are not intended to be user replaceable, and you could very well end up destroying your MacBook Pro trying to swap out a new part on your own.
On the bright side, Apple says you can recharge the built-in battery up to 1,000 times before it's no longer at full capacity. Even if you charged it once every day, that's almost three years of use before it no longer holds a full charge.