David,

He already gave you the power consumption from the electric side. That is already taking the efficiency in count.
Rule of thumb, 50% overall efficiency.
So, if you are modifying something similar to the 24, you will need component rates for that power needs (always over rate).
The batteries won't modify all the others component. If in the future there are better cells, you can change the packs only and save weight.

Regards

Emir