Background/Purpose Implantable loop recorders (ILR) are increasingly used in cardiac rhythm monitoring and diagnostic work-up of unexplained syncope. ILR battery longevity according to manufacturers’ product performance specifications typically ranges between two to four years, but real-world data in this population are lacking. Methods This monocentric, prospective, observational study included consecutive patients with unexplained syncope undergoing ILR implantation between 10/2007 and 10/2019 The main purpose was to determine real-world battery longevity of ILR. Diagnostic yield and relationship between arrhythmogenic diagnosis and duration of ILR-monitoring was explored. Results The study included 309 patients (59 years [38-73], 49% female) with ILR implantation for unexplained syncope. Median battery longevity was 42 [40-45] months. 99.5% of ILR reached prespecified battery longevity. The time to end-of-life varied by up to 33 months among the same ILR models. Overall arrhythmogenic diagnostic yield counted 27% (73% sick sinus syndrome, 20% atrioventricular block and 7% ventricular tachycardia). Median time to diagnosis was 10 [2-25] months, with the latest event at 43 months. The cumulative diagnostic yield for arrhythmogenic event was 15.7%, 22.9%, 34.9% , 54.2%, 72.3% and 100% at 1, 2, 6, 12, 24 and 48 months respectively. In univariate analysis, 1 ^st degree AV-block and prolonged HV time on EP study were predictors of diagnosis, while QRS duration abnormality borderline missed significance. Conclusions Real-world battery longevity of ILRs matched industry projected longevity in 99.5% of patients implanted with ILR for unexplained syncope. A battery longevity of minimum 3.5 years is recommended to maximize the diagnostic yield in this population.