A loaded hobby meter will have a simple resistive load like what we have talked about. It is likely to be a high power resistor, say 5W+. The voltwatch as others have mentioned provides realtime indication and the RX etc acts as the load. Since on a voltwatch there is only ever one LED on at a time the current draw is probably in the order of about 10mA ie <5% of the load drawn by the RX and servos. Consider it this way, on a standard 600mAh pack the single LED drawing 10mA will take 6hrs to discharge the pack. Compare this to an hour or so that we normally get out of the pack during normal flying we can see that the LED will have little impact on the flight time.