If you review the iFixit batteries
[product|IF117-046-5]
[product|IF117-048-5]
You’ll see the power values are different!
While Apple did stick with the same dimensions and the connection to the logic board is the same for both. The chemistry of the batteries is different as such the charging rate programed in micro-controller and SMC what match up properly. I suspect some of the battery failures we have seen are do to the wrong battery being used.