From Longman Dictionary of Contemporary Englishspare key/battery/clothes etcspare key/battery/clothes etcMORE/EXTRAa key etc that you keep in addition to the one you usually use, so that it is available if the one you usually use breaks, gets lost etc a spare key Bring a towel and some spare clothes. a supply of spare batteries a spare tyre → spare
Examples from the Corpus
spare key/battery/clothes etc• It may include parts of larger support weapons such as mortars, radio equipment and spare batteries.• Some people take a fully charged spare battery along with them just in case!• Carrying spare batteries could be a cheaper option to fast charging and all chargers rely on a power point anyway.• I'd got no money, no night things, no spare clothes, no bank card.• Soon she took my visits for granted and I was given the spare key to let myself in the door.• Make sure you have a supply of spare batteries too.• Eventually, the spare key was found and they were released from the clutches of the car.• Remember that I had always intended to leave spare key with the Twills next door but never got round to it. 