Then take one that can take about 80% of the generator power and feed that into the battery bank. Size the charger to the lower of both numbers.

80% feels like too much.

My electric car has a 1600 W charging mode. My emergency gasoline generator supplies 2100 W theoretically if the power factor is 1 (totally resistive load). When I connect my charger in 1600 W mode, the generator trips and drops the load, however. It manages to work at 1200 W or below. And this happens despite the charger having a slow ramp-up behaviour (it doesn't go to full load in a second, but during 5 seconds).

So based on experience, I would advise to pick a charger that can take 50..60% of the generator's power.

For a 24V lead acid battery, look for chargers designed for warehouse equipment (forklifts), wheelchairs, truck batteries and such.