Everyones eyes are different, they usually get dimmer the older we get, I'm 68 years old and I don't need 800 or so lumens on a dark bike path, in fact all I run is 500 lumens, the only time I go into the 1,000 lumen setting is if it's a dark bike path and it's raining. But that is bike path, on gravel you might want to see more detail by using a brighter light.
Magicshine makes a light called the Monteer 6,500S Zues, yeah, that thing put out a huge amount of lumens, but it's not the lumens that you need, it's the run time, and if you run that light at 1/4th power, which would still be over a 1,000 lumens, then it should run for about 8 hours since it will run at full power for 2 hours...HOWEVER, I'm guess, so you would want to email Magicshine directly and find out how long it can run at various brightness levels.
Lumicycle light actually tells us how long each lumen level will run for their Apogee light. If you get their largest 6.8 Ah battery it can run at 1000 lumens for 10 hours, the max brightness of this light is 4,500 lumens which you would never need but it would run for 2 hours at that level, if you kick it down to 400 lumens it will run 27 hours, those run times are not for flash mode, they are for steady mode! That light is the longest run time light I could find, the others wouldn't say.
https://lumicycle.com/product/apogee/ This light comes with different packages, small and large battery, slow or fast charge, you obviously want the large battery, but I would not opt for the fast charger, fast charging will shorten the long term life of the battery. This light isn't cheap, but trying to get run time that you need with decent brightness isn't going to be cheap.
The other long lasting light is the Light & Motion Seca Enduro, on its low setting at 650 lumens it will run for 10 hours, not quite as long or as bright as the Lumicycle light in the higher modes however, but the Seca is cheaper.
If those lights are too expensive then it would be cheaper to get a light with a replaceable self contained battery that you can buy a couple and simply change out the battery during the ride, or you can get a light with a separate battery pack and simply buy an extra battery pack. A light like the Cateye Volt 1,700 uses a tool free battery cartridge, this light will run for 5 hours on the middle setting at 500 lumens, so two batteries would give you 10 hours of run time, the extra battery is around $125 plus $276 for the light, which puts the price into the Light & Motion Seca Enduro range! So I would get the Seca at that point.
Anyway, just some ideas.