Battery subsystems now have their own FDR.
As do iPods and Apple Mac laptop batteries!
I took my iPod to an Apple store about 5 years ago to have them check out an intermittent fault. They told me that I hadn't used it for over 18 months and when I asked how they could possibly know that, they told me that prior to a full charge that day, it had not been charged since 3 March 2006 at 18.23.
Apparently every charge/discharge cycle during the life of the battery is logged with the battery itself. :-)