lol whys that?
Or take the money that he would be wasting and put it to better use.
If his voltage drop isnt that bad, then something as little as a D975 Or D925 would be better of then a cap, In my opinion.
He has no use for another battery if he is staying at a constant 14.4v, and adding one would not fix the problem, which is caused by the charging system not being able to supply power at a rapid spike... Which the capacitator would be able to do... IMO...
BUT, he wouldnt be at 14.4v constant..... so your whole theory is flawed...