I've replaced the battery in my 2013 15" mbp... and I have the old one(s).
They're free to any hacker who might have a project that could use some batteries. The connectors and what not are super custom, of course, but someone with sufficient knowledge might be able to do something useful with these like a UPS for a rPi or something.
Free to anyone! I can leave it at Sector for you, or if you're in a hurry, you can pick it up in Madison.
(If nobody wants this, what's the safest way to recycle?)
Thanks!
Here's a screen cap of the battery info right before I removed it from my computer:
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