Only thing I can say is that this is futuristic right now for the Altima.

I do not even know if a Camry Hybrid has yet been converted
to a plug-in. Only about 200-300 Prius have been converted.
A few Escape hybrids have also been converted but that's about
it.

You will be the pioneer for the Altima if you do it and will be
exploring some uncharted technological challenges.

It may still be doable by a knowledgeable engineer and a there
are some case studie available as to how to do it for the Prius.

Look at this site:
http://www.calcars.org/howtoget.html