Would you buy a new battery for a very old laptop?

I just got a pretty good deal on an old ThinkPad (think 10 years old now) to use as a beater for screwing with ArchLinux and hopefully to find a real use for. It's in great shape like it was never really used, but big shock, the battery is at 50% effective capacity and what's there disappears in less than an hour.

Would you bother buying a battery replacement for it? On one hand I want it to actually be usable on the go because that was sort of the point. On the other, while replacement batteries exist, I'm worried that they're already very old themselves and already "expired". Would you take the chance? I don't want to let this thing go to waste when it's still perfectly usable, in fact it's pretty fast.