Tinkering with the old Sturmey archer bicycle dynamo, I was wondering
whether it would charge a 1.2Ah SLA any better if the loading was modified.

The generator is rated 6V/3W, but off load at a decent rate of knots it can
produce over a couple of hundred volts.

What I was wondering was whether its possible to get more energy into the
battery by letting the generator output voltage stretch its legs so to speak
and convert the excessive voltage down with a buck converter.

Can anyone advise on the practicality of this please?

Thanks.