I don't think charging lead-acid batteries is as critical or dangerous as charging the more-modern batteries.
I think you just "pump" current into it by applying more voltage than the current charge-state voltage.
So you need slightly-more than the battery's rated voltage available, and then you need to control/limit the current (so you don't burn-up the charger. (The voltage will "fall into place" for whatever it needs for that current at the moment.)
Do some research on lead-acid batteries and on how to build a constant-current switchmode (1) power supply, or you can make a "normal" switchmode power supply with current limiting. Constant current power supplies are commonly used for LEDs, but 1000W is "unusual" for an LED supply.
1000W is a LOT and it WILL generate as much heat as a 1000W toaster or hair drier. It might be too much for the battery. You'll probably have to "slow down" the charge by feeding-in less energy.
In case you don't know this, power (wattage) as calculated as Voltage x Current so at 48V, 1000W is about 21 Amps.
You don't really need an Arduino (or any programming) for a charger, but it could be useful if you want to monitor and display the voltage & current, or if you want to build some more advanced logic into it.
(1) Switchmode power supplies are the most efficient and the most practical & economical way to get high-power. But they are not easy to build. 