You can also get NOS batteries on eBay for virtually nothing. Recently got a 68+ for my T440 for £39 delivered.

Be careful though as anything over 4 years old can be DOA as the batteries slowly discharge and the BMS in the battery itself disconnects them permanently for safety. This applies to ones Lenovo sell as well. I found this out when I bought the above but the seller sent another one out FOC. I dismantled the dead one, pulled the 18650s out and charged them up standalone and they were fine. Free cells!

The big problem with NOS battery is that sometimes its a gamble! I bought one off eBay for my x230 and I had to change it.

But the seller was cool enough to change it ( getting 4-5 hours ) and a smaller one which gets me around 2 hours more.

Yes it is a gamble but as I said, it is from Lenovo as well. The battery manufacturing date I got from a "new" one was 4 years old once.