I would say its worth it to get the battery for now. Hard to say where the PC market is going and honestly things don't look great, but if its still working then I would say the battery should hold you over in case things do get better for the PC market.
While you're in there you can also clean it out and reapply thermal paste so that it helps the CPU and GPU (if it has one) last a bit longer as well. Might even boost performance a bit.