The bios for the XPS 13 (9343) has some great sounding settings available to optimize the long-term life of the battery. In particular there is a "Custom mode" that suggests you can set an upper limit to not charge above, and a lower threshold at which to start charging.
Sadly, it looks to me like these settings are ignored. I set a 40% lower limit and 80% upper limit, but when the battery is at 75% and the ac adapter is plugged in, the battery charges anyway. I was expecting it to not charge.
Am I misunderstanding this "Custom" setting, or does it just not work? I've tried BIOS A02 and A04.