Ex: Nominal voltage is 230V an you read a consumption of 1A so the power is 230W but if the delivered voltage is only 220V (a +- 10% variation is totally normal) you will consume 220W but the reading will still be 230W. I think it's not good enough to make tests.
Using DMM has the added advantage you can also use it to test DC power and isolate sub-systems (Processor power consumption from the 4pins 12V, or graphic card with external power) It would be more accurate than simply measure the total power consumption of the system.
But thank you for the good work you are making by giving us reliable benchmark; you can only optimize what you can measure!
With ThinkPads and the "tp_smapi" kernel module you can discharge the battery even with AC connected by writing a "1" to "/sys/devices/platform/smapi/BAT0/force_discharge" (switching back to AC can be done by writing a 0 or automatically when the battery is empty). So your laptop won't power off when you got the AC adapter inserted and the discharging forced.with still needing to monitor them for manually toggling the AC power / battery
This way you could at least automate the "charge/build new kernel/wait until battery has reached >50%/reboot - switch to battery - measure - switch to AC" cycle with accurate (and easy!) measuring.
More info (with hardware compatibility matrix) is here: http://www.thinkwiki.org/wiki/Tp_smapi
Last edited by jannis; 06-03-2011 at 08:30 AM.