@Iroh I’m not sure if this has been covered, a quick search of this thread didn’t bring anything up:
Is the new Pro series battery more robust, at a “lower level” (battery controller logic/limits, or even cell/chemistry level), than the previous gen 61Wh battery?
Background: The 61Wh battery that was originally introduced with the 13 7040 series suffered from a premature aging issue when kept at/close to 100% charge state (laptop plugged in for days on end use pattern). Although all Li-Ion batteries will suffer from this, I think this particular battery was a little more sensitive until the BIOS charge limit and battery extender features landed to mitigate it:
I can attest to the success of the mitigation: I’ve had my 7840U for 2.5 years, docked the vast majority of the time, charge limit set to 70%. Battery is at 24 cycles, no swelling, and battery life on occasional unplugged use seems fine.