I am looking for information on battles in Spain during the period of the 100 Years War
A Good primer is
War in the Iberian Peninsula, 700–1600 (Themes in Medieval and Early Modern History) April 2018
by Francisco García Fitz (Editor), João Gouveia Monteiro (Editor)
There is a paperback edition of this at about £35.
There are some very expensive Brill volumes on the subject, edited by Donald Kagay e.g. To Win and Lose a Medieval Battle Nájera (April 3, 1367), A Pyrrhic Victory for the Black Prince
João Gouveia Monteiro has also co-written a book on Ajubarrota available as a free download in Portugese https://www.academia.edu/37024257/Aljubarrota_Revisitada .There is an English translation but it is £70. Monteiro is enthusiastic about accessible versions of his papers on Researchgate and Academia but mostly in Portugese.
Thanks