Longest night ride 5 hours, wore out my first battery in about 4 and went to the back-up to get home. Reason was just to ride, when darkness falls at 5PM the only time to ride was at night so there was no purpose other than the ride. I actually enjoy riding more at night, cars seem more observant, courteous or puzzled by the lights and give me a wide berth. Traffic is less or non-existent, wildlife abounds and trails are empty. It's also cooler on those hot humid summer days.
Like you said though, back up lights are the key, I carry two good headlights, and a EL300 as a last resort, along with spare blinkies should the need arise, had one of those vista-light rectangle shapes the inevitably pops apart, ususally I hear the parts hit the ground, but if I miss the sound, I have spares in case.