Apple's price is not $139, it's $129. There are aftermarket batteries available, some of them dirt cheap. Avoid those. They're likely to be worthless, as many other dirt-cheap replacement notebook batteries are. I don't recall seeing anyone recommend any particular third-party replacement here, and my own original A1281 is still in fair shape, so I have no personal experience with any of the aftermarket units. But for more than 12 years I've been reading unhappy posts in these forums from people who paid half or less than half what Apple charges for Powerbook and MBP batteries, and got much less than they paid for.