What I wonder is:
(?) Is OP a native English speaker and is this word used in daily contexts,
(or?) did he use it because he might not be an English speaker and he searched for the words in his own language and that is the word that came out, instead of the more common "tirelessly".
(or?) he is a native speaker and he knows this word is not used in daily/common conversations... so, by using this different concoction, did he meant to translate some additional feeling? is "indefatigable" a stronger "tirelessly"?
I know it's oddly specific but I am not a native speaker and insight into these odd ducks helps me build a maturer mind model of it all.
Thank you.