I fly a lot and rely on the on-board power to get my W500 through a transcon or international flight. I got the W500 instead of the W510 solely because of the availability of the travel adapter. I actually bought a W700 and returned it immediately, it was like the clown shoes of laptops, ridiculously over-sized: both the laptop (absurdly larger than the apple 17") and the power cinder block (several times the volume of the compact 90W adapter, too big to be a "brick").
I'm very curious if run time can be extended meaningfully by using the 90W adapter in combination with batteries in the W520. It would be extremely helpful if someone would undertake the following experiment:
Run the W520 on battery alone for normal laptop tasks and report runtime.
Run the W520 on battery plus 90W for similar tasks and report runtime.
(bonus points for running it down with some standardized test suite to improve the accuracy of the results)
extra bonus points for running the same experiment with the 135 W adapter
Double extra bonus points for testing on plane power.
My experience so far:
Older KID DC-DC systems (still in use on many planes) can drive 120W power adapters. This is sufficient to run the W500. I don't have a 510/520 to test. The batteries charge normally. It will also run the compact 90 AC/DC adapter through the DC cable.
Newer Astronics systems (AC plugs, labelled "Empower") will sometimes drive the 90W AC compact travel adapter (41R4538), but not always. I fly United so my tests are on their planes. I've learned that UE/UB/UF classes may have different power limits, but the maximum is 75W per seat pair if both people are using the power, or 90W if the person in the seat next to you isn't using power.
Different planes seem to be configured differently. This is possible - there are several Astronics units: the 1215 which puts out 150VA per outlet and the 1191 which can supply 200VA per outlet. This may explain why some planes barely run the W500 on AC (generally the batteries charge fine in sleep mode, the computer can sometimes run at minimum power draw, but will trip the breaker reliably if the batteries are discharged and the computer is running in "performance mode.")
However, in most first class cabins on transatlantic flights, on the one continental domestic first 737 I've flown recently and most UAL PS flight business cabins (but not all) the plug-in power works fine and will charge the laptop while running.
It would be awesome if Lenovo would add a "plane mode" and travel charger for the W520 which would use as much power as available, with a software controlled throttle to allow setting the maximum wattage drawn through the adapter before tripping a breaker, so those of us who fly AND need a powerful computer can get as much work done as possible.