How can I check battery life on iPod Original 5th gen?

I am writing a book series! this is most commonly caused by the battery not providing the feedback needed. It (the battery) was not as smart as the now common smart batteries. So, in order to truly test the battery it needs to be taken into consideration that the battery condition is also dependent on :

battery connector

battery fuse

battery charge and discharge FETs

battery cell pack

battery sense resistor

battery primary and secondary protection ICs

battery fuel-gauge

battery thermistor

and probably more.

There are some external "battery chargers" that can report charge status, cycle rate etc. but only (again) if the battery IC makes use of that data.