I am trying to troubleshoot battery life issues in OS X Lion on my MBA13. Is there an app (or hidden system information) that can tell me how long my computer has been on since last full charge. I am not looking for uptime, but looking specifically for Time Since Last Full Charge, just as is available in iOS.
You could try MiniBatteryLogger
It helped me troubleshoot my battery issues. I'm not sure it will do exactly what you asked for but when you have it running (on battery or power adapter):
And right now it's even free: