I always bring two headlights ... and at least two tail lights. The problem is, i cannot tell when the tail light dies because it is behind me.
I am sure someone somewhere is devising a tracking system to report on battery life, etc. and it only weighs three pounds and costs $200.
As with so many other topics here ... I am sort of glad I never got the memo that riding a bicycle was so fraught, so dangerous, so difficult ... I just go ride and enjoy it. i didn't realize I was doing it wrong.