Correct spelling, explanation: the form warranty is correct because it originated from Old French as warantie, meaning protection or safeguard. It has its roots in the Germanic language spoken by Franks. The word warranty crossed the English Channel in the 14th century and nowadays it has legal use. Consequently, the form warranty is exclusively correct.

Definition of warranty:
noun, a countable noun that means guaranty and security that a certain obligation will be fulfilled
When you buy a new television, take an extended warranty.
It is good to buy an extended warranty that covers accidental damage.

Phrases with warranty:
year warranty,
You have to five-year warranty, a free advance replacement program, and the support of our service.
warranty card,
Yes, I have a warranty card but it has expired for two months.

Incorrect spelling, explanation: since the word warranty comes from Old French as warantie, the form warrenty is incorrect. The users of English may misspell this word due to its pronunciation. The word warranty is articulated as [ˈwɒr(ə)nti]. This vowel can be sounded as e but the users of English should memorize that in this place, the letter a is written, not e. Therefore, warrenty is spelled incorrectly.

Incorrect spelling