Just some info about batteries. For our modern enough skyline cars our alternators output it sufficient enough generally 70A+ to choose essentually the biggest battery you can fit (length and width)with correct terminals, venting requirement, orientation in a pre-detemined space from generic retailers(lead acid). Height should be equivalent of OEM to prevent fouling or non-conformance to ventilation requirements.
Best battery to buy for r33 cheap is a 67ef or equavalent (EF falcon) that will bolt in. I usually change to large terminals as there is a bigger variety and generally cheaper pricing. I also connected a second earth.