There are quite a few storage compartments in the Z4, one under the passenger seat, so have a good root around them. It could also have fallen down the side of the battery. If stuck, send a picture to this ebay seller https://www.ebay.co.uk/itm/355476143887?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D265237%2C265303%26meid%3Dc9f04df664ab4edfb1b97fe3a7b99c57%26pid%3D101875%26rk%3D2%26rkt%3D12%26sd%3D386434454110%26itm%3D355476143887%26pmt%3D1%26noa%3D0%26pg%3D4429486%26algv%3DSimplAMLv11WebTrimmedV3MskuWithLambda85KnnRecallV1V2V4ItemNrtInQueryAndCassiniVisualRankerAndBertRecallWithVMEV3EmbeddedAuctionsCPCAutoWithCassiniEmbRecallManual%26brand%3DUnbranded&_trksid=p4429486.c101875.m1851&itmprp=cksum%3A355476143887c9f04df664ab4edfb1b97fe3a7b99c57%7Cenc%3AAQAJAAABgP9d%252BMZSXlztIfYFu3kI%252B7ft0VcQix7rTrUVdiJwc2upzwLfM%252B2UEqu0ZqdXqu2qWe6up6s9MSEY%252BWikIwEh4xLkizL%252BG%252Fyhg6cdW4xfkbb75erVQBYYISNxGN1au%252BE0eJ778JYYSAyLJRupNiZky3B2UHpMsaEp7JRgW9fuueOszPlG9eCPE4mSzJx4EejjZE0v1xx3s4HgKujjhEB3s6l1mG7abzOsoVEne6TqSpvu4H79Xp%252F8mM4pMlFIfLeQWtSXdRMl%252Bt5IZieHhm0tIPeTiLUGHxSRan5SJ%252B3a07fVEMpDT8uL6uWFH8ypOWX5U8anIMbLxQ0Tsp8y1KLLa72oOm90M2dPUG84Q6vUBCp6Ve4H59ttmqO%252F2LcQE9c7sxP8QFaC3nl815YBz4blsx0vEqNymdugvze7AeN00nEKJx8Q7E3XOtVkKjgjED7lNxlMwN1t7HwPHgoVMFj%252FuTnJYf1CbRZBdMoKU8wrgPZDQoG2gH5ltcrJzAwps76GgQ%253D%253D%7Campid%3APL_CLK%7Cclp%3A4429486&itmmeta=01HX9WX60RRYCPRZ485FACNMS8