Mellow has a new BattOr firmware that should help with problems with communicating with it. But, I think the bigger bug here is that after it fails its not returning and the job times out.

For subprocess timeout, we should use https://cs.chromium.org/chromium/infra/luci/client/utils/subprocess42.py?q=process42&dr=C&l=5

Is the job timing out? I'm seeing the whole task took something like 2m30s. Am I looking at the wrong thing?

I think what's going on here is a test failure and not a timed out

2m30s counting run time and processing time for the benchmarks seems reasonable. It is not timing out. The communication with the BattOr fails during the 120s test. This might be fixed with the new firmware:
https://codereview.chromium.org/2956903002/

I'm going to postpone looking at this bug for a day until we have more data points after the new firmware that Randy released yesterday.

I'm gonna go ahead and close this. I think this is just a manifestation of some other timeout issues that we're seeing with the BattOrs, and it looks like the power.idle_platform timeout actually worked as expected (only taking 2m30s to run).