IF you add up the wattage that the headlights & parking lights use..then subtract that from the battery's rating you can figure how long it will last.

Each headlight uses 45-55 watts.
Each parking bulb uses 10 watts, side markers & tag lamps as well.
2 headlights = 100 +- watts
8 parking lamps = 80+- watts
Almost 200 watts including the interior lighting....divided by 12V =16+ amps on a battery rated at 80-100 amps.

I would think a good battery would last 2 hrs at that rate before not having enough power to start the car!

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