They are normal 3.7v li-ion polymer cells. Probably 2px3s (2 in parallel, 3 in series) So you could use them for lighting leds. There are hundreds of chargers/chargerboards for these kind of batteries on AliExpress or Ebay but you’ll probably need to do some soldering.
And of cause you need a driver for the leds if there is not already one included.
Maybe you can sell the battery. There are a lot of MacBooks with bad batteries out there ;)