Surface Book 2 batteries

Hello guys,

I'm curious about the battery use in surface devices (SB 2 13inch specifically). By the design, any Li-ion battery starts degrading overtime, since Surface Book has two batteries I wonder how does it work once it's running on the battery?

1. Does it use both batteries at the same time when in laptop mode or does it use them individually?

Because Li-ion batteries degrade over time, I feel like it's going to be the same as with any smartphone out there now. Amazing at first, after the first year 10-20% worse and so on. Obviously, it degrades over time on its own, but if charged often or the charger is always plugged in even when the battery is at 100% it helps it degrade even quicker (right?). In any other regular laptop with batteries that can be taken out, I always take them out when I use it at home, because I usually want all the power with no worries about the battery life, but Surface Book battery can't be taken out. So...

2. Does Surface Book have an option or function to use the main power coming straight through the charger rather than the battery (basically to turn the battery off so it's untouched and to use only when it's unplugged)?

Thanks