Almost everything known today about Bathala and the wider Tagalog religious world he headed survives through the writing of the Spanish colonizers who set out, in the same period, to dismantle that world. The single most important early source is the Franciscan friar Juan de Plasencia's Relacion de las Costumbres de los Tagalos, written in 1589, barely two decades after Spanish colonization of Luzon began in earnest, which describes Bathala Maykapal alongside the anito spirits, the babaylan and the offerings and taboos structuring Tagalog religious practice, information Plasencia gathered specifically to help fellow missionaries identify and suppress what they were converting people away from. That origin gives the record a double character: it is close enough in time to pre-colonial practice to preserve real ethnographic detail, yet produced entirely by observers whose stated purpose was the religion's replacement, not its preservation, so later historians read Plasencia and similar accounts carefully rather than treating them as neutral description.
Spanish Catholic evangelization proceeded rapidly across the Tagalog-speaking lowlands over the following century, and organized worship of Bathala as such did not survive it as a continuous, living priesthood the way some other regional traditions did. What remains beyond the missionary chronicles is folklore, collected mostly from the nineteenth century onward, in which Bathala persists chiefly as a figure in origin stories and children's tales rather than as an object of formal cult, and modern Filipino cultural and religious movements have drawn on both the colonial record and the folklore in reconstructing and discussing pre-colonial Tagalog belief.