A few additional comments...
Fatiguing the battery: I assume it's about fatiguing the T71 battery, not the Laptop battery, correct?
The T71 has two power modes, "USB VBUS" and "HYBRID". In either mode, you can enable/disable charging. So, in VBUS mode, it either charges from the USB source (Plus sign in the battery current display/Chrome Ext.)... or not if the battery is fully charged, or if you disabled charging (0 mA current). In Hybrid mode, it takes power mostly from the internal battery (Minus sign in the battery current display/Chrome Ext.), but
can take power from the USB source... if you enable charging and the battery is low, or--not sure about that--if it needs an extra power "boost" (in addition to the internal battery).
This is a quite complex power management, but
@Tano is correct, in VBUS mode, the T71 never pulls energy from the internal battery.
Unlike the 5K, the T71 does not offer the option to limit the charging to 80% to preserve the battery life... but the battery is replaceable
). It appears fairly easy to replace:
View attachment 351253
You mention more power... T71 certainly has more available power than the 5K, but in my experience, the 5K bal. mode is more than adequate to power about all my headphones except, perhaps, my 600 Ohm DT990 (Not even sure, as I seldom use it...). To me, the main practical benefit of the T71 is the addition of a 4.4mm output besides the 3.5 and 2.5mm output.
One last thing, you indicate desktop/sofa use: the T71 is not as "sofa-friendly" as the 5K IMO. It is much bigger & heavier and I would not leave it hanging from the USB/HP cables as I do with the 5K. Also, the 5K has a shirt clip, usable with a long USB cable... and has BT !!!