How is it set?
First, use proper wiring. Alligator clips aren't, or at least not preferred.
Also, the charge curve of lead-acid is different. You can use a LFP charge, but that's not ideal
First, lead-acid likes (well basicly requires) a float, whereas for LFP float is preferably disabled or at least set to a low voltage to prevent overcharging.
Also, depending on the lead-acid variant (AGM, wet, gel), it requires a higher voltage. Some require up to 14.8V for a 12V pack, which would result in 59.2V for a 48V pack.
The charger can provide only up to 58.4V.. thus it might not be able to work properly with all lead acid batteries (although it's not too big of an issue).
Secondly: Charge curve. A LFP will just take basicly anything due to the flat curve. Only at the very end the voltage starts rising, thus lowering the amps.
A lead-acid however has a different curve. The higher the SOC, the higher the voltage (much more compared to LFP). And with a higher voltage there is less of a difference between charger and battery... and a difference is required for any current to flow.
It's not uncommon for lead-acid to charge with high amps when empty, and fasty decreasing current when even a little full. 5A near full doesn't sound too strange to me. Off course it depends on the total capacity how the exact figures would be.
I'd set the voltage as high as possible (58.4V) and see how it goes. It's unlikely you're getting the full 25A till 90% SOC, but that's more generic to LFP than a issue with the charger: Thats one of the benefits of LFP..
Lead acid charging isn't capacity / charge amps = time, while its (almost) fine to do so for LFP, especially at high charge rates. Also keep in mind that lead acid doesn't like high charging amps at all.
200Ah lead charging with 50A: not only probably something like 0.2C charging max (which you're exceeding) its more likely it takes 6-8 hours to FULLY charge.
200Ah LFP with 50A: 4 hours, slightly more, but not off by much.. and generally acceptable, since charge can be 1C, 0.5C or so adviced. Well within specs.
If you're going with the lead acid for a while, better get a different charger for the time beeing, which also allows proper float to keep those batteries topped up properly.
As for the generator: That one is having a hard time... 58V / 25A is 1450 watt.... Your's is only 1000W.
Even at 48V / 25A your generator isn't able to handle it. It will shutdown or worse.
For generator sizing it's recommend to have the required power x2 as rating, so you should have something like 2.8-3kW at least if you want to run it for extended times and not killing the generator fast..
Due to the low charging amps with lead-acid, you might be lucky and be able to run the 1000W just fine, but it's still a guess. With a LFP you need to either upgrade the generator, or downsizing the charger if you want to run it at all (or not want to destroy the generator)
