My ZJ is a 2nd hand offroad modified one and the battery drains for some reason. Mechanics I have showed it to didn't give a **** since they never see a 4+ cylinder engine in this part of the world anyway and noone I know likes cars

The steering wheel also sits in a slightly slated angle which makes it awkward while driving, mechanics said that the only way is replacing the steering box(?), any ideas ?

Steering wheel angle is easy. There is an adjustment sleeve on the drag link. Loosen the nuts on it and use a pipe wrench to rotate it. It will make the problem better or worse. If worse, go the opposite direction with rotation. May take a couple of tries, but you will get it. First thing to do with the battery is disconnect it and see if it loses charge. If so, replace it. If not you will have to start pulling fuses until it doesn't drain. That would be the circuit with a drain and then you will have to decide why

Welcome!

Dunno what to say about your steering problem. If he steering box is really making your steering wheel sit at an odd angle, something is really wrong.

As for the draining battery, check this out:

You're talking about the steering wheel not being straight rotationally when the jeep is going down the road, correct? That can be fixed by adjusting the threaded end of the drag link where it attaches to the pitman arm (Arm that is attached to the steering box output shaft.) To move the steering wheel clockwise, you loosen the clamp sleeve, disconnect the drag link from the pitman arm, and turn it a couple of turns to make it longer. You make it shorter to turn the steering wheel counterclockwise. Only turn it a couple of turns before driving it to see if you did it right or wrong and how far it moved. When you are satisfied, tighten the sleeve clamps and torque the pitman arm tapered connection.

Too many mechanics when replacing a link end will "count the turns" it takes to remove the old worn end and install the new end the same amount of turns. It's much more accurate to measure the length of the rod between the grease fittings and make the new one match. There are way too many variables in the production of the forged end links to assume they are all the same length, regardless of manufacturer.

Beware bad tires, will cause pull to one side. Swap the front tires with each other and see if it reverses. Just went through this a couple months ago. New Cooper AT tires and boom, steering all lined up again.
As for the infamous ZJ battery drain, what I found with assistance from a knowledgeable dealer tech, and my multi-meter in 10A current mode, is there "were a LOT of problems with the switches on the two front doors and the tailgate" not working. Tiny little plastic deals that sit on the back of the external key lock. You may notice issues with this in the security system not arming, and or interior lights. Either way if a switch is broken in the 'unlock' position, the body control module with see that and not let the vehicle go into sleep mode where it should only use about 14 milliamps. ( .014 amps ) Rather it will hang around closer to 1 amp if I recall. That will drain the battery surely.