Is there an app that will track "Time since last full charge" on OS X?
Everything you need is provided with OS X.

For graphical details and an overview, open Activity Monitor and the energy tab lists the time you have been on your current power source:



In my case, it was showing 5 hours on AC power, so I disconnected the charger to show that the battery is just starting up. The graph on the right will give you a nice history if you go between multiple charge/drain events over the last 12 hours.

For details, use the pmset command in terminal app:

pmset -g log


Since that log is verbose, you might start with filtering the messages about Using

pmset -g log | grep Using