The laptop I used for the test was a reasonably old Compaq and the charger is not the original one which came with it (the original died a few years ago). I leave my laptop charger almost constantly plugged into the electrical socket in the wall, but for the purposes of the test I connected it through the Individual Appliance Monitor as shown in the picture.
- I checked the power consumed by the laptop charger when there was no laptop attached and like the phone charger it was consuming 0 watts.
- I waited until the laptop battery was well drained and then I plugged it in. The charger immediately started to consume about 63/64 watts of power.
- I put the laptop into sleep mode, but the power consumption of the charger did not decrease (presumably because it was still busy charging the battery). After 2 hours the power consumption gradually decreased to 1/2 watts but not to 0. I assume that this is because the laptop is still consuming power in sleep mode. To eliminate all power consumption I would need to either unplug the laptop or else put it into hibernate mode.
- The charger consumed roughly 0.05 KWh to charge the battery fully. At current electricity prices in Ireland this would cost slightly less than a cent.
- When I woke the laptop from standby the consumption went back up to 24 watts. I assume this is because the charger is providing live power to run the laptop, but not needing to charge the battery.