An extra battery can not be hot-swapped, right? But, an external battery can just be plugged in to take over as the regular battery runs low. Then, an external battery can potentially charge the regular battery and run the laptop simultaneously, right? Granted, not all external batteries are designed for this, and accumulating weight and pieces might be an issue.
This article is >4 years old:
External Battery Roundup: Stay Away From The Wall Socket
MAR 8, 2011 - IN ARTICLES > COMPONENTS
Does anyone know where there is a current comparison table(s) or new strategies for running a laptop longer "in the field"? I want to run a T540p, 15.6" laptop.