Thanks for the suggestion. After that change, the GPU now does run on battery power without crashing the system.
But under batter power it’s running at about 1/3 the speed.
(This is measured in training samples processed per second. I’m running NetTrain on Wolfram Mathematica with GPU target). This effect is reversible and repeatable. I can unplug and plug in the power jack multiple times, and it will slow down and speed up accordingly each time.
This change also disables the NVIDIA X-server settings utility, which was handy for monitoring GPU use.