This problem is not related to BMS, but either EC or the topology of the computer’s hardware.
Here’s my guess:
Most “classic” laptops have one DC power input socket, 18~20V mostly 19.5V via DC5525. Said laptop can only be used with the AC adapter provided by the manufacturer, or if you have a bench power supply and you set the voltage/current correctly.
On these laptops, the power rail is connected directly to the 19.5V input. Then there are some DC-DC converters mounted on the 19.5V rail, to convert voltage to 5V, 3.3V, ~1V(VRMs) and of course, the battery.
The distinctive characteristic of these laptop, is all these AC adapters can provide power for maximum instantaneous load AND charging the battery with plenty(20%+) of headroom. In this case, the battery is merely a component of consuming power. Removing the battery does not affect the stability of the circuit. If the AC adapter is overloaded, it’ll turn off and the laptop runs solely on battery, hence the mandatory “headroom” of the AC adapter power rating. “Bypass charging” is inherent.
The problem with USB-C powered laptop is that to comply with PD standard, the laptop must be compatible with a variety of AC adapters with different power rating. To achieve that, a buck-boost DC-DC converter must be installed between the input and the power rail. This introduce a problem: non-instant response. When the load spikes, battery power is taken until the upstream DC-DC reacts, even if the load is lower than the input power rating.
For instance, you can draw up to 90W from a 100W input, with 45~75W load, charging the battery 45~15W, but you cannot draw more than 57W if the battery is removed, read the reply above for more information
There are bugs in BMS in random batches, like charging slowly below 25%, charging slowly below 21°C, only charge to 17.4V(should be 17.6V on 55Wh), discharging quickly below 25%, but they are not the cause of small charge/discharge cycle(see above). The reason is due to the lack of a direct connection to the power input, the laptop cannot use more than 33/37/57W with 60/65/100W adapter without using the battery as a buffer.