"Is the battery replaceable?"に関する回答The battery is replaceable. You just remove the back with a + screwdiver and pull out one plug, plug in new battery and plug in. Really simple. Watch out for static
"Is the active pen supported?"に関する回答The 15.6" screen size does not have the active pen (wacom digitizer). The 14" model had it as an option but is no longer available. And not all 12.5" models do either - it is an option. I personally find the digitizer tremendously helpful but the precision is not as good as the MS Surface Pro especially in the edges.