noun
extended warranty
A service contract that prolongs the warranty period beyond the standard coverage, common for electronics and appliances.
このテレビには延長保証を付けることができます。
You can add an extended warranty to this TV.
延長保証に加入しておけば、修理費用が無料になります。
If you sign up for the extended warranty, repair costs will be free.
Compound of 延長 (extension) and 保証 (warranty). A straightforward modern term with no obscure historical derivation.