The fact that the question has been asked, suggests that the OP's DIY skills may be limited. While batteries may appear to be innocuos, they can store a large amount of energy. The habitation battery fuse must be relocated to a position close to the battery, and the existing cabling extended, or prefferably replaced, with suitably sized cables. Given that a lithium habitation battery is proposed, I would suggest 16 sq mm, as a minimum. With consideration being given to 25 sq mm.
Changing to a lithium battery is not a simple switch, if full benefits are to be obtained. The existing mains charger may not have a lithium profile, and to gain maximum charging rate from, and to protect the alternator, a B2B charger should be fitted. If the maximum recharge rate is required, then an alternator with a higher output rating may be required. In this context I have seen mention that alternators are rated at peak current, and not continuous current, which is what a lithium battery could draw.