The point is, that getting out a single value that would somehow be "not false", is probably not possible.

Within a single 10 second interval, the device might consume very little or very much power, depending on what is happening right now. So with a short interval you would just get an estimate that alternates between 2 hours and 2 days every 10 seconds (in the most extreme case). With a longer sample interval to average over, the measurement will get a bit less erratic, but will still suffer from the fact that the difference in rate of consumption between idle and in use is like the difference between flushing the toilet and a waterfall.

A more feasible scheme might be one that was in N810. It gave two different estimates, "active time" and "idle time".

Code for what you are requesting should be quite simple to do, for example with a small Python script, but would provide a number that is not much better that throwing a pair of dice, or the current "false" estimate you get with lshal.

Edit: Ok, based on your another comment here, it seems that "active time" estimate is what you're looking for...