I have not seen this reported so I wanted to share my experience and observations. I have an original 13" with an updated CPU and expanded memory. I use an ethernet expansion card at home so I can hardwire to my LAN for throughput.
Recently I traveled and left the card attached. I found that my battery drained pretty quickly when the laptop was fully off if I left the card plugged into the slot. Here are some stats which illustrate and quantify the issue. This is based on upower reports (in Linux) taken before shutting down and after booting up.
Updated comparison table
| Test | Duration | Card | Avg. power drain |
|---|---|---|---|
| Fri 17:48→Sat 08:39 | 14h 51m | With card in | 0.146 W |
| Sat 10:16→Sun 08:44 | 22h 28m | No card in | 0.012 W |
The battery consistently drains when the laptop is off and the card is in. The solution is obvious: it’s just a matter of remembering to take it out when shutting down unless it is left on power while turned off.