Recording to SD card?

I have tried to search for the answer but I cant seem to find one, sorry if my searches were bad.
I have a problem with my car in that either the alternator or the ecu is failing but both garages I have been to even a specialist can’t tell me if its the alternator or ecu!!!

Basically the ecu is reporting voltage spikes. So what I want to do is to record say 30 seconds (ideally more) of the battery voltage when I startup the engine. Looking at a version 1 nano it appears that it would do the job but I can’t find a definitive answer as to if I can store a waveform on the SD card or can it store say 15mins of a voltage trace to the SD card?

Sorry for such a noob question but only just found the nano.