Bike battery to power DC or AC devices.

Hi all,

I am about to live in the car for 1 month, private reason.

I have two ebike batteries, both 48V-15Ah (so 1500Wh in total).

I am searching the way to power some devices: (1) Cool box of 12V, 48W, (2) Laptop, etc

If possible, I even to power also this: (3) Rice cooker (220V, 505W)

For (1) and (2), LLMs told me to buy the Buck (Step down) converter to convert from 48 to 12V, however I don't know how to connect that converter to the bike battery.

But the ebike battery doesn't expose an easy interface for me, it only has 4 or 5 "racks", and its base does know how to read from those 4-5 "racks" but I don't want to cut the wiring of the base to bring into the car.

For purpose (3): I don't dare to dream yet, though I would love to. Currently while driving the DC-to-AC converter pulls power out of the car's main 12 V battery to feed the rice cooker, but I'd like to power up the bike battery for use when not driving.

How to ?