Gauging battery drain.

I know this has come up before, but...

Short of just installing on device and checking battery level at intervals, is there really no way to gauge battery drain?

I know watch faces with onPartialUpdate can view diagnostics when in low power mode, but nothing similar for per minute / low power updates. 

It would be really useful to have a similar feature for low power mode where partial updates are not done so as to be better able to compare coding techniques.