Honestly, mostly I'll buy Lenovo-branded batteries on eBay for these things and hope they're new old stock and not counterfeit (or are at least high quality regardless). That is the biggest worry I have about using older laptops though; spec-wise, an old used laptop can honestly be just fine for a lot of people, myself included.
I'm glad hobbyist projects like this exist, but I wish they didn't have to.
I'm glad hobbyist projects like this exist, but I wish they didn't have to.