I think my title succinctly asks my question. I primarily intend to use my Surface Pro 3 as a tablet as a scientific lab notebook, taking notes on experiments, entering data, taking pictures of setups, and also in meetings for notes, and for reading journal article PDFs and taking notes. But, at times I think I will 'replace' my desktop by using a mini displayport to hdmi adapter. I'm trying to figure if I need an extra charger for work. I assume if I plug SP3 into a external monitor and set its screen to turn off that battery life will be much longer? How much active use do you guess I can get in this mode with activities like using MS Word and the internet? Thank you.